The last time the Mississippi River was this high for this long, it prompted the federal government to build the modern levee system.

The river has been in flood stage for months, and on Tuesday, will hit 136 days in flood stage at Baton Rouge, breaking the record set in 1927.

What's more, the river is still in major flood stage and rising, though held in place by the levees. Meteorologists say they expect it will stay in flood stage "well into summer."

The persistent high water has had economic and ecological ramifications. Construction work near levees has ceased, and excess river water passing through the Bonnet Carré Spillway, some experts say, has posed a threat to marine life and to Louisiana's seafood industry.

Officials say the levees are holding after being shored up since the 2011 floods, though some are waiting to see whether sink holes form when the water recedes. The U.S. Army Corps of Engineers doesn't expect to open the Morganza Spillway, but it says it has been close and it's keeping an eye on forecasts.

Maj. Gen. Rick Kaiser told Pointe Coupee leaders and landowners last week that the Corps has "no intention" of opening Morganza but said the crowd should keep going to church and praying.

The river is so high in large part because it's been at least 124 years since the eastern half of the country has gotten so much rain, Kaiser said.

"Why 124 years? Because that's when we started keeping records," Kaiser said. "Are we wet? Yeah. Is this business as usual? No."

National Weather Service hydrologist Jeff Graschel said the closest the river has gotten to this level of flood in the modern era was in 1983, when the Mississippi was in flood stage for 115 days.

Areas such as the Tennessee River Valley saw record rainfall in the past year, and the Midwest also had a wet fall, so the river never really got low around November, as is typical, he continued.

The typical formula the Corps uses to predict flood stage doesn't even apply because the water has been so high for so long, Mississippi Valley Watershed Chief Joey Windham said.

Nevertheless, south Louisiana's levees are holding, said Col. Michael Clancy, of the Corps. His New Orleans District has noted more than 200 points of concern, including more serious issues with erosion near Louisiana State Penitentiary at Angola and a sand boil in Pointe Coupee Parish.

The Mississippi River is held in place not just by the levees, but by the Old River Control Structure upstream of Baton Rouge on the Mississippi state line. Without it, the river would jog over to the Atchafalaya River channel, but the Old River Control Structure ensures that 70% of the combined Mississippi and Red rivers flow down its current path.

The Corps has embarked on a three-year study expected to cost between $3 million to $5 million to study how best to employ the facility during normal and emergency operations, Clancy said.

Overall, he said, there are "no major problems right now."

Clay Rives, director of emergency preparedness for East Baton Rouge Parish, agreed with Clancy's assessment.

Rives and Corps officials independently said if any problems crop up, it likely will be due to an accident such as a construction crew breaching the levee or a barge crashing into its side.

Should that happen, East Baton Rouge Parish has 10,000 prefilled sand bags and can work with the Louisiana National Guard to deploy larger "super" bags about 4 feet on a side from helicopters, Rives said.

This year's response has gone smoothly because Congress dedicated funds to strengthen the levees following the 2011 flood, Rives said.

"We expected to have more issues" this year, he said. "We haven't had any so far. ... So far, we've been very fortunate."

Other areas are holding their collective breath.

Many Mississippi River leaders were in Baton Rouge last week for a conference about the dead zone in the Gulf of Mexico. Conference attendees said the dead zone this year could be the largest on record because of the farm fertilizer and other nutrient-rich material the high water is carrying into the Gulf of Mexico.

But Mississippi River mayors are also worried about the other impacts of flood.

Vidalia, north of the Corps district that includes Baton Rouge and New Orleans, is seeing river water seep underground, Mayor Buz Craft said. He's worried about the impact to the town's sewerage system and that once the water recedes, sink holes might form under roads, which could tear up the infrastructure and put drivers in danger.

Places like Caruthersville, Missouri, are already recording sink holes believed to be related to high water, said Colin Wellenkamp, director of the Mississippi River Cities and Towns Initiative.

The high water is also preventing new roads from being built.

During a flood response, the Corps restricts construction near levees to make sure heavy equipment doesn't cause a breach. However, the restrictions have been in place so long, authorities haven't been able to move on road and trail projects near the river at St. Gabriel since October, Mayor Lionel Johnson said.

In a broader sense, all the wet weather also hurts farmers who ship their goods through south Louisiana ports, said Mayor Kevin Smith, of Helena, Arkansas. Standing water limits where they can plant, and the extra moisture breeds disease and rot, he said.

"How long can you sustain that? You can't predict your losses if you can't predict the weather," he said. "This weather is uncharted territory."

The historic flooding has also spooked the seafood industry. The Mississippi has gotten so high, the Corps has had to open the Bonnet Carré Spillway twice in one year for the first time.

The influx of cold, fresh water affects wildlife, though there's no consensus on the precise extent. Mississippi state officials blame the opening on a rash of dolphin deaths, reasoning that the introduction of fresh river water hampers the animals' ability to communicate and navigate, causing them to get lost and die.

Authorities generally agree that opening the spillway does lead to die-offs of creatures important to the seafood industry.

"We haven't seen crabs and shrimp in (Lake Pontchartrain) and the surrounding areas like we should, and if the upcoming shrimp season doesn't produce, that should be a clear indicator that our fisheries are facing a disaster due to the freshwater," Tommy's Seafood Vice President Chalin Delaune wrote in a news release.

Follow Steve Hardy on Twitter, @SteveRHardy.