Mississippi authorities are blaming the Bonnet Carré spillway for the dead dolphins and turtles washing up on their shore, though Louisiana officials are contesting those claims, and federal scientists are withholding judgment until they know more.

The U.S. Army Corps of Engineers is increasingly reliant on opening the spillway to divert high water from the Mississippi River toward Lake Pontchartrain to prevent flooding around New Orleans. The Corps has opened the gates in three of the last four years, including a 43-day stint that concluded earlier this month.

The Corps did not respond Tuesday to requests seeking comment. Louisiana Wildlife and Fisheries staff said they haven't heard of any efforts to change how the Bonnet Carré is managed; the decision to open its bays is based on Mississippi River water levels.

But allowing so much fresh water to drain into the Mississippi Sound is hurting wildlife, said Moby Solangi, director of the Institute for Marine Mammal Studies in Gulfport, Mississippi. He estimates that so far this month his group has encountered 25 dead Kemp's ridley sea turtles, an endangered species.

The IMMS will also perform necropsies on dead dolphins that have washed ashore; 45 have been found in Mississippi so far this year, said Erin Fougeres, administrator of the marine mammal stranding program for the National Oceanic and Atmospheric Administration's regional office.

Mississippi averages 32 strandings — including dead animals — between January and April, and while the number this year is up, it hasn't risen high enough to prompt an official federal investigation, Fougeres said. Her office is keeping an eye on the situation but Fougeres is reserving judgment until all the veterinary results are in, which could take weeks or months.

Louisiana officials, meanwhile, have said that opening the spillway can hurt oysters and slow growth of shrimp, but that larger, more mobile animals can simply swim away.

In a way, allowing Mississippi River water to spill over toward Lake Pontchartrain mimics how the river would have behaved before the levees were built, said Martin O'Connell, director of the Nekton Research Laboratory at the University of New Orleans.

Fougeres explained how freshwater intrusion could potentially hurt animals like the bottlenose dolphins that live off the Mississippi coast: When salinity drops, it affects the animals at a cellular level. Skin cells can't regulate the amount of fluid inside them. They balloon up and deteriorate, allowing bacteria and fungi in, where they can cause infections and lesions. Dolphins stick to their home territory and are reluctant to move, even when faced with destruction, as evidenced last year off the Gulf coast of Florida where many died during a red tide outbreak.

Too much fresh water can also damage the animals' eyes and alter their blood chemistry, but the lesions are a clue that fresh water is affecting them. Several of the dolphin carcasses that have been examined showed lesions, and others were too decomposed to tell one way or the other, Fougeres said.

Solangi blames the opening of the Bonnet Carré, saying he saw similar fallout when it opened in 2011. Fresh water that enters the Gulf via the Mississippi River mixes easily with the salt water, but the relatively slower leak from Lake Pontchartrain into the Mississippi Sound means the fresh water just sits and stagnates, he said.

The Mississippi Department of Marine Resources did not provide a comment Tuesday, though they have previously told the Biloxi Sun Herald newspaper that freshwater intrusion is damaging oyster reefs, as happened in 2011.

Patrick Banks, a Louisiana Wildlife and Fisheries assistant secretary, agreed that using the spillway has been linked to oyster die-offs. However, because the bays were opened earlier this year when the water was cooler and left open for a relatively short amount of time, the state isn't expecting as big a hit to oyster populations, he said.

Too much fresh water can stunt shrimp growth, which could lead to a later or less impressive season, Banks said. Fishermen, crabbers and others in the seafood industry may have to find their catch in new places, but "they've been through spillway openings before," he said.

Some species even like an influx of fresh water. It's a boon to cypress swamps, said Louisiana Wildlife and Fisheries Assistant Secretary Randy Myers.

O'Connell, the UNO researcher, agreed. When he studied the spillway in 2008, he found that animals fled from the spillway water more because it was cold than because it was less salty. Bigger fish were able to get away, but less mobile invertebrates suffered some damage. Spillway openings have dampened blue crab fisheries, but those have typically rebounded within a year, he said.

O'Connell allowed that at times, the rapid changes in temperature and salinity can push already stressed animals over the edge. Sometimes, however, the spillway must be opened or New Orleans would be at flood risk, and the water diverted toward the Mississippi Sound is behaving like it would if the Mississippi River were allowed to flood naturally, albeit at a faster pace.

This time of year is also rough for dolphins, Fougeres said. The animals have just had their calves, and both exhausted new mothers and young dolphins are less resilient. The last two carcasses were both immature, she noted. Gulf dolphins are also still dealing with the aftermath of the Deepwater Horizon oil spill. Animals that survived the initial disaster have chronic lung disease, lower body weight and possibly heart problems, which could make them more susceptible to other stressors like colder, less salty water, Fougeres said.

While the recent debate has centered on salinity, an LSU researcher is also preparing to investigate the impact that opening the spillway has on potentially dangerous algae. The Mississippi River carries nutrients as well as water when it's redirected toward Lake Pontchartrain. That can lead to algae blooms when the weather is warm and the water is still, said Sibel Bargu Ates, associate dean at the College of the Coast & Environment.

This summer she'll study the preponderance and toxicity of Lake Pontchartrain cyanobacteria, a type of algae that can harm the liver and irritate the skin. She hopes her research will shed light on factors that make cyanobacteria more toxic and what effect it has on animals and humans that eat affected seafood or swim in water where the algae is present. Ates has asked the Corps to provide funding to allow continued monitoring during the warm months when cyanobateria is present.

Follow Steve Hardy on Twitter, @SteveRHardy.