<img class="styles__noscript__2rw2y" src="https://s.w-x.co/util/image/w/bonnetcarre2016.jpg?v=at&w=485&h=273" srcset="https://s.w-x.co/util/image/w/bonnetcarre2016.jpg?v=at&w=485&h=273 400w, https://s.w-x.co/util/image/w/bonnetcarre2016.jpg?v=ap&w=980&h=551 800w" > Louisiana's Bonnet Carré Spillway is made up of 7,000 individual wooden pins, or "needles." The spillway could be open soon for the second time this year. (Bob Henson/Weather Underground)

At a Glance The spillway protects New Orleans from flooding.

The Mississippi River is rising due to unusually wet weather in the Midwest.

The Bonnet Carré has never been opened twice in one year. Rising waters in the Mississippi River could lead to another historic weather-related event: the opening of the Bonnet Carré spillway, about 27 miles upriver from New Orleans, for the second time this year.

The spillway is located in St. Charles Parish. When open it helps protect New Orleans and other downstream communities from floods by diverting waters from the Mississippi River into Lake Pontchartrain and on to the Gulf of Mexico.

It was opened earlier this year for just the 13th time since 1937, according to Dr. Jeff Masters of Weather Underground.

(MORE: April Has Been an Extreme, Record-Breaking Weather Month From Coast to Coast)

The spillway was closed again on April 11, but as the Mississippi continues to rise, the U.S. Army Corps of Engineers is considering opening it again, The Times-Picayune reported. If so, it would be the first time the spillway has ever been opened twice in one year.

Whether that decision is made will depend at least in part on upcoming rainfall forecasts for the Mississippi River Valley, Corps spokesman Ricky Boyett told the newspaper.

“We are projected to be close to the trigger, but will need to closely monitor what is happening in the valley over the next week before we have a better understanding,” Boyett said.

The Lower Mississippi River Forecast Center in Slidell, Louisiana, predicted Monday that the river could rise to 16.9 feet in New Orleans on May 11 and stay at that level for three days. The spillway is generally opened when the water reaches 17 feet, according to the Associated Press. Much of New Orleans' levee system has been rebuilt since Hurricane Katrina to withstand waters up to 22 feet.

The Mississippi typically rises every spring, but has been trending higher in recent years, according to researchers at the Woods Hole Oceanographic Institution.

This year is no exception, thanks to heavy precipitation in the Midwest.

"Any rain that falls in the upper and mid-Mississippi River Basin flows southward toward the lower Mississippi River Basin before draining into the Gulf of Mexico, so the rainy conditions upstream have caused river levels to remain high near New Orleans," weather.com meteorologist Brian Donegan said. "The Mississippi River also drains many of the smaller rivers in the Plains and Midwest, which have also been running high this spring due to an abundance of rain."

NOAA's Climate Prediction Center is forecasting above-average amounts of precipitation over parts of the Mississippi Valley for at least the next few weeks.

When the spillway opened in January, it marked the first time it had ever been opened in two consecutive years.

The logistics of opening the Bonnet Carré aren't easy. The spillway is made up of 350 gated bays, each with 20 wooden pins, or "needles." The 7,000 needles must be pulled out one-by-one by a crane, although typically only some of bays are open. The process can take several days, according to The Times-Picayune, depending on how many of the needles need to be pulled.

Use of the spillway also comes with environmental concerns. The Biloxi Sun-Herald reported last week that freshwater that flowed from the Bonnet Carré spillway into the Gulf of Mexico over the 43 days it was open so far this year may have caused the deaths of at least 13 dolphins and 23 sea turtles along the Mississippi coast. The freshwater intrusion has also been blamed for damage to oyster reefs.