[Updated 4:15 a.m. Friday] Isaac, now a tropical depression is working its way up the Mississippi River Valley, bringing heavy rain and the threat of flash floods to the area. A tornado watch remains in effect for much of Mississippi. Parts of Arkansas and Mississippi are under flash flood watches and warnings, according to the National Weather Service.

[Updated 10:35 p.m. ET] And finally ...

[tweet https://twitter.com/artfAEMA/status/241326843901407232%5D

[Updated 10:21 p.m. ET] The folks who catch the shrimp we enjoy on our tables are a tough lot, a breed apart. Not a few of them rode out Isaac on their boats.

[Updated 10:09 p.m. ET] Electric utility Entergy says it will bring its Waterford 3 nuclear plant back online over the coming days. The plant, 25 miles from New Orleans, was shut down Tuesday as a precaution as Tropical Storm Isaac approached. About 41 percent of all homes in Entergy's Louisiana service area were without power as of late afternoon.

[Update 10:01 p.m. ET] Louis Armstrong New Orleans International Airport received its first post-Isaac incoming flight this evening, from Aspen, Colorado, Mayor Mitch Landrieu's office says.

[Updated 9:54 p.m. ET] The Salvation Army says it has provided more than 8,000 meals, 7,000 drinks, 6,000 snacks, and emotional and spiritual care to nearly 600 individuals along the Gulf Coast during the storm period.

[Updated 9:44 p.m. ET] New Orleans Saints quarterback Drew Brees tweeted a message of support for the folks back home while the Saints prepared for a preseason game against the Tennessee Titans in Nashville:

[tweet https://twitter.com/drewbrees/status/241293012414652416%5D

[Updated 8:39 p.m.] Storm surge and high winds pushed several pleasure boats out of Mississippi's Pass Christian Harbor, leaving vessels high and dry on streets and in parking lots, CNN affiliate WLOX reports.

"I'd say in one word, it's a mess," Pass Christian Mayor Chipper McDermott told WLOX. "We had 215 boats in the harbor, and all but six or seven got out. As you can see, three are in the road, and that is a big problem."

Boat owners were under orders to remove their vessels from the harbor before the storm struck. McDermott wants to have a word with those who didn't.

"I'm personally taking it upon myself to talk with these boat owners," he said. "I'm personally doing it."

[Updated 8:21 p.m. ET] CNN iReporter Gerard Braud submitted a video report from from the floodwater underneath his elevated house in Mandeville, Louisiana. His generator and lawn mower washed away, he says, and his tool shed moved from one side of his yard to the other.

[Updated 8:08 p.m. ET] A tornado that dropped down from an Isaac feeder band destroyed a home in Pascagoula, Mississippi, Thursday morning, CNN affiliate WLOX reports. The home's elderly residents were not injured, the station said.

"I was actually coming out the side door of my house to get the truck and head to work and this tornado that caused all this damage came through," neighbor Billy Perkins told WLOX.  "You could see it coming right across these rooftops behind me, through the tops of these trees and hit down on the next house over and just literally exploded the roof off the house."

[Updated 7:43 p.m. ET] With the downgrading of Isaac to a tropical depression, the National Hurricane Center has stopped issuing updates on the storm. All coastal watches and warnings have been discontinued. The storm's sustained winds have dropped to 35 mph, but the system has picked up speed, now moving north-northwest at 12 mph.

[Updated 7:24 p.m. ET] The city of Little Rock, Arkansas, is making sandbags available to residents as Isaac's rains approach, CNN affiliate KARK reports. The city sits next to the large and meandering Arkansas River. Firefighters are handing out sandbags in the city of Conway; those bags are being filled by prison inmates, CNN affiliate KLRT reports.

[Updated 7:03 p.m. ET] Water rescues continue in low-lying areas inundated by storm surge and heavy rain.

[Updated 6:50 p.m. ET] According to the mayor's office, New Orleans' Causeway and Twinspans bridges are open, but several roads and bridges remain closed: I-10 at LaPlace; U.S. 90 around Rigoletes; I-55 by Ponchatoula; and the U.S. 11 Bridge.

[Updated 5:12 p.m. ET] Strong winds and storm surge from Hurricane Isaac's landfall forced the Mississippi River to flow backward for nearly 24 hours on Tuesday, the U.S. Geological Survey said Thursday.

The USGS stream gage at Belle Chasse, Louisiana, showed the Mississippi flowing upstream at 182,000 cubic feet per second, surging to 10 feet above its previous height. Average flow for the Mississippi River at Belle Chase is about 125,000 cfs, toward the Gulf of Mexico, the USGS said.

"Although it doesn't happen often, hurricanes can cause coastal rivers to reverse flow," a release from the agency said. "Between the extremely strong winds and the massive waves of water pushed by those winds, rivers at regular or low flow are forced backwards until either the normal river flow or the elevation of the land stop the inflow."

Storm surge from Isaac has been observed as far north as Baton Rouge, USGS said.

"This reversal of flow of the mighty Mississippi is but one measure of the extreme force of Isaac," said USGS Director Marcia McNutt. "While such events are ephemeral, they are yet another reminder of why we need to respect hurricane warnings."

[Updated 5:03 p.m. ET] About 13,000 customers have lost power in Arkansas as Tropical Depression Isaac approaches the state, CNN affiliate KARK reports.

[Updated 4:45 p.m. ET] Red diesel fuel that washed ashore Thursday morning in Biloxi, Mississippi, came from the fuel tank of a generator at Keesler Air Force Base, CNN affiliate WLOX reported.

Officials said the diesel leaked into storm water, then drained into the Back Bay.

"Once we came out here and actually smelled the diesel fuel and confirmed it, we started immediate recovery teams," Col. Mark Vivians with Keesler Air Force Base told WLOX. "We actually have a contractor coming online to do full recovery of this area and actually capture the diesel fuel and remediate it."

[Updated 4:38 p.m. ET] Isaac is no longer a tropical storm and has weakened to a tropical depression, the National Hurricane Center says.

[Updated 4:31 p.m. ET] Utility company Entergy says on Twitter it has 1,100 people working 16-hour shifts to restore power in the storm-affected region.

[Updated 4:23 p.m. ET] Emergency responders are assessing the dam at Lake Tangipahoa at Percy Quin State Park in Pike County, Mississippi. Heavy rains from Hurricane Isaac damaged the structure, but it has not been breached, Gov. Phil Bryant's office said.

"Heavy equipment and pumps from across the state have been dispatched to initiate a controlled water release from Percy Quin State Park to the Tangipahoa River to relieve dam pressure, which should not significantly increase water levels down stream," the governor's office said.

Mississippi residents south of the dam have been encouraged to evacuate the area until the dam has been secured.

Louisiana Gov. Bobby Jindal confirmed his counterpart's statement: "As we're speaking the folks in Mississippi are  in the  process of intentionally breaching the dam over in Mississippi," Jindal said at a news conference. "The intent is to allow 8 feet of water  to come out and then reinforce the structural integrity of the dam. If this is successful, based on modeling, ... that would  not have significant effect on water levels down here."

The water is being released into a heavily wooded area, Jindal said.

[Update 4:08 p.m. ET] There will be no curfew in New Orleans Thursday night, the mayor's office said. The airport is still closed until power can be restored. Streetcars are not running, but many bus routes are operational. Weather permitting, normal garbage collections should resume Friday.

[Update 4:01 p.m. ET] [tweet https://twitter.com/GOHSEP/status/241258426775252993%5D

[Update 3:47 p.m. ET] "It doesn't take but a little breach (in a dam) to make a big problem for all of us," Tangipahoa Parish, Louisiana, President Gordon Burgess said at a press conference. "That water will move south quick."

Burgess, Gov. Bobby Jindal and other officials urged residents within a half-mile of the Tangipahoa River to evacuate the area immediately as a dam was in danger of failing, releasing a flood of water.

[Updated 3:27 p.m. ET] All roads and bridges within the New Orleans levee system are open, with some isolated lane closures, Mike Stack of Louisiana's Department of Transportation and Development says. Ferry service remains suspended.

[Updated 3:19 p.m. ET] Country singer Reba McEntire is raising awareness about relief for Isaac victims:

[tweet https://twitter.com/reba/status/241222241671585792%5D

[Updatee 2:57 p.m. ET] Victims of the flooding in Braithwaite, Louisiana, talk to CNN affiliate WWL about their harrowing escapes.

[tweet https://twitter.com/usNWSgov/status/241235182324183041%5D

[Updated 2:50 p.m. EY] Louisiana Gov. Bobby Jindal has just called for the immediate evacuation of the town of Kentwood, CNN affiliate WWL is reporting.

[Updated 2:43 p.m. ET] More than 915,000 customers in Arkansas, Alabama, Louisiana and Mississippi have no power, utility companies tell CNN.

[Updated 2:40 p.m. ET] Forecasters predict that the weakening Isaac will be a tropical depression by this evening. Torrential rains continues to drench the Gulf Coast.

[Updated 2:36 p.m. ET] Officials are pumping water over the dam near Lake Tangipahoa and digging a hole into it - an intentional breach - to relieve pressure on the structure, the Mississippi Emergency Management Agency says.

The agency doesn't expect a catastrophic event, said MEMA spokesman Greg Flynn.

The state has "a good number of prisoners there ready to begin sandbagging if it comes to it," Flynn said.

[Updated 2:18 p.m. ET] We have a couple of nice offerings from Anderson Cooper and Soledad O'Brien. One is a report on how the destruction caused by Isaac in Plaquemines Parish was far greater than that wrought by Katrina. Also, Cooper and O'Brien chat with members of the self-styled "Cajun Navy," private citizens who used their own boats to perform rescues after Isaac struck.

[Updated 2:02 p.m. ET] Let's stop for a cuteness break. If you were following the live blog yesterday, you may have seen an iReport about an 8-year-old leaving a set of instructions for her stuffed animals while she, her brother and mother evacuated ahead of Isaac.

Well, iReport has caught up with Ashley Taylor, who says the media is making a big deal over nothing. She just wanted to make sure her furry friends were safe while she was gone, she said.

From her Gammy and Pawpaw's house in Mobile, Alabama, she told iReport the rules "just came to me." Asked why she forbade the stuffed animals from throwing soirees in Rule No. 4, she replied, "Because they’ll mess up my room and then my mom will get mad at me."

She added that she is a little embarrassed by all the attention.

[Updated 1:53 p.m. ET] The bridge that connects Dauphin Island to the Alabama mainland has been washed out by water and debris, and it may be Friday before officials can start clearing the causeway, CNN affiliate WPMI reports.

On Wednesday, a boater had to be rescued from his sail boat because of the nasty conditions on the water. The abandoned ship still had its sails raised, and it floated down toward the Dauphin Island Bridge, where it hit a power line that pumps electricity to the island’s 1,200 residents.

The residents are still without power, WPMI reports.

[tweet https://twitter.com/JasonWhitely/status/241229548702818305%5D

[Updated 1:38 p.m. ET] In other levee news, Plaquemines Parish President said earlier today that officials planned to breach a levee on the east bank there to relive pressure after Isaac brought massive flooding to the area.

Gov. Bobby Jindal just said during a Baton Rouge, Louisiana, news conference: "We are proceeding with plans to purposely breach that levee today between 2 and 3 p.m. The idea is to allow that water to flow out of that area. Now that the winds have shifted they're planning on having pumps on site to help de-water that area as well."

[Updated 1:31 p.m. ET] Gov. Bobby Jindal says Mississippi officials plan to intentionally breach the dam near Lake Tangipahoa to prevent if from breaking.

The river stood at more than 17 feet this morning, more than 2 feet above flood stage, according to the National Weather Service, which predicted the river could reach 19.5 feet by tomorrow.

Near Kentwood, Louisiana, in the evacuation zone, the river could reach 17 feet, which is 4 feet above flood stage. Officials say an intentional breach would send water into a forested area rather than Louisiana towns, Jindal said.

[Updated 1:19 p.m. ET] We're focusing pretty heavily on the situation along the Tangipahoa River right now, but remember we have a state-by-state breakdown of situations unfolding in Louisiana, Florida, Mississippi and Alabama.

[Updated 1:13 p.m. ET] The Terrebone General Medical Center in Houma, Louisiana, is short on Type O blood, according to CNN affiliate WWL. All types of blood donations are welcome at the hospital's Blood Donor Center, but the need for Type O is most critical. If you're in the area and able to give blood, please call  (985) 873-4025 or (985) 873-4029 to set up an appointment.

[Updated 1:09 p.m. ET] The Tangipahoa Parish government has issued a statement on its website saying the dam is damaged but not broken. It says there are shelters at Hammond West Side Elementary Montessori School, Hammond Junior High Magnet School, Natalbany Elementary School, Nesom Middle School, Amite High School and Kentwood High Magnet School.

Gov. Bobby Jindal will hold a news conference at the parish's Council chambers at 2 p.m. CT, the statement says.

An emergency alert beneath the statement calls the dam's failure "imminent."

[Updated 1:03 p.m. ET] While there have been operations all over the southeastern portion of Louisiana – including the overnight evacuation of about 150 people in Plaquemines Parish – rescue efforts homed in on St. John the Baptist Parish last night, said Louisiana National Guard Lt. Col. Mike Kazmierzak.

High-water vehicles, local police and troops evacuated more than 3,000 people, and those efforts are still ongoing, he said. They are heading to shelters throughout the state.

“They’re getting out of harm’s way,” he said.

[Updated 12:54 p.m. ET] In July, the Enterprise-Journal in McComb, Mississippi, reported that Percy Quin State Park officials planned to work on the dam some time after this coming Monday.

The plan called for Lake Tangipahoa to be drained 6 to 10 feet so the dam and spillway valve could be "reworked," the paper reported, citing park manager Will Busby. The project was slated to take all winter.

[Updated 12:46 p.m. ET] The Louisiana Emergency Management Agency says that if the dam fails, water levels along the Tangipahoa River near Kentwood could quickly reach 17 feet.

[tweet https://twitter.com/WAFB/status/241212014805016576]

[Updated 12:39 p.m. ET] Looks like the confusion is cleared up. The Mississippi Emergency Operations Center says the dam near the 700-acre Lake Tangipahoa has been damaged by heavy rains, but water has not breached the dam.

You can read a PDF of the center's statement here.

Gov. Bobby Jindal says the evacuation order pertains to people within a mile of the Tangipahoa River and is urging everyone in the area to heed the warning.

[tweet https://twitter.com/GOHSEP/status/241205173370888192%5D

[Updated 12:10 p.m. ET] Pike County Civil Defense's latest Facebook update says: "Flood warning for the Tangipahoa River at Osyka. The dam at Lake Tangipahoa, better known as Percy Quin State Park, has been damaged by the torrential rains from Hurricane Isaac, but is intact, and is not leaking. We are monitoring it. All residents below the dam that live along the Tangipahoa River are being notified of the damage."

[Updated 12:07 p.m. ET] As of about 20 minutes ago, a National Guard helicopter was maintaining position over the dam to monitor its integrity, The Times-Picayune reports. As of 11:45 a.m., it was still holding, the New Orleans paper reported.

[Updated 12:03 p.m. ET] The National Weather Service is reporting that the dam is "expected" to fail.

[tweet https://twitter.com/NWSNewOrleans/status/241203654152052736%5D

[Updated 12:01 p.m. ET] OK, so a small conflict in reports from officials near the Tangipahoa River.

Despite early reports of an apparent levee failure near Lake Tangipahoa, which is close to the Mississippi-Louisiana state line, Mayor Whitney Rawlings of McComb, Mississippi, says Pike County Civil Defense informed him that "the dam is holding, but they are concerned it may fail," WWL reports on air.

He further said it's a coin toss whether it will fail, but, "This might go. People need to be moving now."

Bear with us as we work out the discrepancy in the reports and work to determine whether the dam has failed or is expected to fail.

[Updated 11:55 a.m. ET] Amite, Louisiana, Police Chief Jerry Trabona tells CNN affiliate WWL on air that officers are going door-to-door to residenc s along the Tangipahoa River after a mandatory evacuation was ordered following an apparent levee failure.

[Updated 11:53 a.m. ET] In New Orleans' Central City neighborhood, police arrested six people Wednesday for allegedly looting in the wake of Hurricane Isaac, the Uptown Messenger reports. Police thanked residents in the area for their vigilance in reporting crimes as they were in progress.