Scientists from the National Marine Fisheries Service are searching the eastern half of Lake Pontchartrain for 35 dolphins that might be endangered by rapidly freshening water.

The opening of the Bonnet Carre Spillway on April 11 as a flood control measure on the Mississippi brought an influx of fresh water into the lake. The mammals need the saltier water to survive, said biologist Kevin Barry, of the service's marine laboratory in Pascagoula, Miss.

When the salt content of the lake's water dropped because of spring rains last year, many of the dolphins experienced potentially deadly lesions that were reported to the agency, which has been monitoring the endangered species since then.

The animals seemed to recover as the lake became more brackish during the year and at least two newborn calves were spotted among the adult dolphins this spring, Barry said.

The dolphins have likely lived in the lake for more than a year, probably lured through passes by the promise of a variety of fish species.

But once west of the U.S. 11 bridge and a nearby Norfolk Southern Railroad trestle, the dolphins seemed to shy away from swimming back east and out of the lake, said Blair Mase, the Fisheries Service's southeast regional stranding coordinator in Miami.

The scientists theorize that they find the narrow passages between the trestle legs uncomfortable, or the bridge itself too low to the water.

The Army Corps of Engineers has agreed to both assist in monitoring the dolphins and, if necessary, to help relocate them to saltier waters by herding them through one of the passes into Lake Borgne.

If that fails, the Fisheries Service may have to capture and relocate the dolphins individually, Mase said.

Beau Gregory, a zoologist with the Louisiana Department of Wildlife and Fisheries, said aerial surveys indicate the pod may actually have moved back and forth between the saltier Lake Borgne and Lake Pontchartrain during the past year.

"Around the time last year they were showing signs their skin was getting better, our people were doing aerial surveys for other things, and they've seen dolphins on the other side of the bridges," he said.