Tom Smart, Deseret News
FILE—Rick Halliday casts at Rockport Reservoir while fishing with his son, Nick, the Utah Water Quality board due to act on a plan to address the nutrient pollution that is killing the oxygen levels at Echo and Rockport reservoirs that are part of a system that delivers drinking water to more than a half million people Wednesday, June 25, 2014, in Summit County.

WANSHIP, Summit County — People should steer clear of areas of scum along the eastern and western shores of Rockport Reservoir, and avoid exposure at the marina's boat launch.

The Summit County Health Department issued an advisory Thursday about the presence of cyanobacteria, or blue-green algae, detected through water sampling.

Employees with the Utah Department of Environmental Quality's water quality division were conducting routine monitoring for E.coli when they spotted the bloom on Wednesday.

They collected five samples at four locations. No large extended bloom existed in the water, but rather the employees observed small olive-green spheres suspended in the water column.

A sample from the main boat launch came back at 7.5 micrograms of microcystin per liter. Microcystin in a potent liver toxin and possible human carcinogen. It can kill livestock and pets that drink the water, and is also associated with fish and bird mortalities, according to the U.S. Environmental Protection Agency.

The health department noted that the blooms are localized and don't affect drinking water, but recreationists should take precautions when visiting Rockport Reservoir.

Although a sample showed the presence of microcystin at the main boat launch, Utah State Parks spokesman Eugene Swalberg said it is safe to launch a boat.

"If you are not prolonging your time in the water, if you are not swimming, not playing in there, you are not going to get hurt by launching your boat and then moving to an area where it is not," he said.

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Anglers can still fish in waters where a bloom exists. People should clean the fish and wash their hands with clean water. Since toxins concentrate mostly in a fish’s organs (fatty tissue and skin) discard those and eat only the fillets.

The Summit County Health Department is working with the Utah Division of State Parks and Recreation, Department of Environmental Quality, Department of Natural Resources, Park City Water, Mountain Regional Water and Weber Basin Water Conservancy to monitor the algal bloom.