Lake Seminole Dolphins?

A freshwater lake with no real access to the ocean shouldn't have dolphins in it, but someone claims to have seen them in Florida's Lake Seminole. From the St. Petersburg Times:

"A reported sighting of three dolphins in Lake Seminole has city, county and state officials scratching their heads over what appears to be an impossibility for a landlocked, freshwater lake.
"The lake does have a weir for outflow, but even then 'there's just no possible way for a dolphin to fit in there,' said Kelli Levy, a Pinellas County environmental program coordinator.
"'They would have to swim through a few feet of water under Park Boulevard, then jump like 12 feet in the air over the weir. I can't think why they would want to do that.'
"Alternatively, Levy said, the dolphins could have been swept into the lake at 10015 Park Blvd. if a 'big, humongous hurricane' came along." ...
"Levy was responding to a plea for help from the city of Seminole, which received an anonymous e-mail last Thursday:
"'At the risk of sounding a little crazy, I would like to mention to someone in Seminole gov't. that at 8 am Wed. 1/31/07 I saw what appeared to be three dolphins swimming in the SW corner of Lake Seminole near Park Boulevard. My girlfriend saw them as well. I thought I should at least report it to someone and found this e-mail contact for Seminole.' It was signed 'Concerned Citizen.'
"A city official forwarded the note to Levy with this note:
"'Have you ever heard of dolphins in Lake Seminole? Is it possible for them to get through the weir from the bayou to the lake? Also, if this is true, we have a problem as these critters are saltwater tolerant.'
"Despite her doubts about the sighting, Levy reported the story to the state Fish and Wildlife Conservation Commission, which dispatched biologist Ken Arrison to the lake in search of dolphins.
"Arrison spent four hours walking around the park Friday and saw 'a lot of humans and a lot of great birds, but no dolphins,' he said.
"If they're there, Arrison said, it's likely they'll be seen again because dolphins have to come up for air fairly frequently.
"Both Arrison and Levy hope 'Concerned Citizen' will contact them with more information. Thus far, he has not responded to requests for comment to his e-mail address from the city, county, state or Neighborhood Times.
"Levy suggested the couple might have mistaken grass carp for dolphin. Grass carp were put into the lake in the late 1990s to eat the grass.
"They reach 35 to 40 pounds and 'they kind of come to the surface and they kind of roll over,' she said.
"Arrison suggested the sighting may have been diving birds. When cormorants dive, he said, their backs will break the water.
"And perhaps, there's one more explanation, Arrison posited.
"'You never know, maybe Lake Seminole has its own Nessie,' he said, referring to the legendary Loch Ness Monster."

Another "dolphin" was reported from Florida's landlocked Gasparilla Lake in 2003. Unless and until better evidence is found, the carp theory is probably the best one right now.