Two of the reservoirs are in the Wasatch Back.
Harmful algal blooms have been reported at Rockport and Deer Creek reservoirs and may sicken people and pets that drink the water.
The DNR warns people to not swim in any water body under the advisory.
Blooms form when naturally occurring bacteria multiply to high densities and form visible water discoloration and mats.
Harmful algal blooms can look like pea soup, spilled paint, grass clippings or water that has a green or blue-green hue.
