TEXAS (CBSDFW.COM) – Biologists are trying to figure out what’s killing turtles — at least 60 so far — in as many as three Texas cities.

First discovered in Fort Worth, possible cases have also turned up near Houston, and in East Texas around Jasper.
Once the turtles are sick, most, if not all of them, are dying. The sick reptiles are lethargic, have blisters and their eyes are swollen shut.

READ MORE: Three Dismembered Bodies Found In Fort Worth Dumpster, Police Asking For Tips

“If you see a location where you have lots of turtles up on the bank, looking like they’re basking, even though it’s 40 degrees and raining outside, that’s probably an indication those turtles are sick,” said Rachel Richter with Texas Parks & Wildlife.

Dozens of turtles across Texas have been found dead or dying in the past four months and experts don’t know why. (photo credit: Justin Sullivan/Getty Images)

Scientists are now monitoring ponds, lakes and other waterways to see if the mysterious illness is turning up anywhere else.

READ MORE: State Fair of Texas Kicks Off Today, Masks Required At Indoor Facilities

The illness is affecting four pretty common species, which biologists said are generally pretty hardy, tough common turtles in the state.

Texas A&M and the National Wildlife Health Center are testing turtles but won’t say exactly which lakes or ponds until they know what’s going on.

MORE NEWS: Irving Man Charged With Killing 2-Year-Old Who Wiped Feces On Him

Biologists don’t want to take any chance of people possibly spreading it to other areas.