The Utah County Health Department is warning recreationists to stay out of Utah Lake near Saratoga Springs after water samples taken at the end of May showed unsafe levels of harmful algae.

It’s the fourth straight year that some part of the Utah County lake has been effectively closed to some types of visitors because of harmful algae. This time, the bloom has appeared near the Saratoga Springs Picnic Area.

Algal blooms are naturally occurring under certain circumstances — such as in hot weather and stagnant water with plentiful phosphorus. But state Department of Environmental Quality spokeswoman Donna Spangler said the blooms become problematic because they can produce cyanotoxins, which can hurt humans and animals.

The DEQ tests bodies of water for unsafe levels of cyanotoxins and passes its findings along to the appropriate health department, which issues public warnings.

Officials warned those going to the affected part of Utah Lake to not swim or water ski. People and animals also should not drink or otherwise ingest the water. Boaters should avoid scum-covered areas, and fishers are advised to clean fish well and discard the innards.

Warning signs have been placed around the affected area. The rest of the lake was deemed OK, according to the warning.