Guthrie city officials have halted all swimming and watercraft use at Liberty Lake after discovering large amounts of blue-green algae."Many of the toxins it makes are toxic to humans, to livestock, to pets," said Dave Hambright, a biology professor at the University of Oklahoma.Hambright told KOCO 5 that the algae usually is not toxic. But when there is a large outbreak from no rain and heat, that's when it becomes dangerous."Right now, we're in a deal, this part of the summer, it's just the perfect conditions to get these types of blooms," Hambright said.Blue-green algae is found in multiple bodies of water around the state, and scientists and officials can't always monitor them all."There's too many bodies of water for scientists to monitor that we ask the people if you go out to your normal swimming hole and it looks super green, if you see things like that, just don't let your pets in the water," Hambright said.The Oklahoma Department of Tourism says a good rule of thumb is if it's green on top, stop.If you've ingested or been directly exposed to the algae, officials urge you to seek medical help right away.