Dogs can become fatally ill after contact with water containing toxic algae. Algal blooms typically occur in lakes, ponds and slow-moving streams that are warm, get plenty of sunlight, and are rich in nutrients like phosphorus and nitrogen. Dog owners should be especially wary of water that may contain this harmful algae, called cyanobacteria, which can be deadly to dogs. Consider alternatives to swimming for keeping them cool at this time of year.

The Virginia Department of Health and the Virginia Harmful Algal Bloom Task Force, which includes the Virginia Department of Health, Virginia Department of Environmental Quality and the Old Dominion Phytoplankton lab, monitor water quality in Lake Anna and other bodies of water in Virginia. An advisory was recently issued for parts of Lake Anna that are experiencing a harmful algal bloom (HAB). Two lakes in Montgomery County, Md. have tested positive as well.

Cyanobacteria may not always be visible, because it can sometimes stay below the water’s surface. But it can also “look like foam, scum, or mats, particularly when the wind blows them toward a shoreline. The blooms can be blue, bright green, brown, or red. Blooms sometimes look like paint floating on the water’s surface. As cyanobacteria in a bloom die, the water may smell bad, similar to rotting plants,” according to the Centers for Disease Control.