SEA BRIGHT, N.J. - Authorities say they need to do more testing to determine what killed a dolphin on Monmouth County's Navesink River.

The bottlenose dolphin, which was found dead on Thursday, is one of about 15 spotted in the river since June It is the third known to have died there.

National Oceanic and Atmospheric Administration spokeswoman Teri Frady says that the animal was an older female with an empty stomach. She says the same dolphin was observed to have been in good condition last month.

Frady says it could take some time to determine whether the dolphin had an illness.

Some environmental groups want the government to approve a plan to move the remaining dolphins from two rivers near Asbury Park, fearing ice on the rivers could kill them.

- AP