U.S. authorities are investigating what could be killing hundreds of fish and other marine animals - including sharks and manatees - which in recent days have been washing up on beaches in southwestern Florida.

"High temperatures and cloudy, rainy days can spell trouble for fish in Florida's marine and freshwater habitats. These conditions can cause fish kills, which are natural occurrences that typically do not cause permanent damage to the ecosystem or to fish populations," the Florida Fish and Wildlife Conservation Commission said.

Even so, the FWC asked in a news release for cooperation from the public in monitoring the deaths of the marine life and determining if the phenomenon is spreading to natural lakes and estuaries in the area "to see if there are problems developing in an ecosystem that might require investigation or restorative measures."

The bodies of the dead animals - which include eels, crabs, rays, trout, tortoises and various kinds of tropical fish - have been turning up in recent days on several Florida beaches, among them the one at Naples, which is considered to be among the most beautiful in the United States with 16 kilometers (10 miles) of sand and crystalline waters close to shore.

Tests performed to date have detected the presence of two types of algae that, although they are not toxic, could have been responsible for reducing the amount of oxygen in the water to the point that it forced the animals to move toward the coast where they wound up being asphyxiated in the shallower and warmer water.