By Pat Jenkins The Dispatch Beating the heat this summer at nine lakes in Pierce County has required keeping an eye out for illness-inducing algae. The lakes have been posted by health authorities with warnings about toxic algae. The scummy substance can make swimmers sick or kill them if they stay in the water too long. It can be fatal for pets, waterfowl and other animals, too. Serious injuries or fatalities haven't been reported, but the Tacoma-Pierce County Health Department is continuing the advisories and monitoring the lakes for algae until further notice. Lakes with the advisories include Ohop, Silver, Spanaway, Harts, Tanwax, Whitman, Twin Lakes, Waughop and Whitman. Most of the postings began in July. Tanwax was the most recent on the list, starting Aug. 13. Warning signs are posted at beaches. They advise: " Do not drink lake water. " Do not swim or water ski in areas with visible algae. " Keep pets and livestock away. " And for anglers, clean fish well and throw away the guts. The algae, also known as cyanobacteria or blue-green algae, looks like green or brown paint floating on the surface of the water and can produce toxins. While it's naturally occurring, it likely has increased due to human activities in and around the lakes, according to the Health Department. Toxic algae can reproduce rapidly in fresh water with the right amount of sunlight, warm temperatures and nutrients. Within a few days, a previously clear lake, pond or ditch can become discolored with the growth, which is called a bloom. The blooms float to the surface and form a scum several inches thick near the shoreline. Wind and weather conditions can change the amount and location of toxic algae. If the algae becomes too prevalent, authorities can close a lake and tell people to stay out of the water. On a recent 80-degree day at Lake Spanaway Park, two children accompanied by an adult played and swam in a shallow area of the designated swimming area that appeared to be free of the algae. Anglers were fishing from a nearby dock. A sign on the beach, near the water's edge, warned the toxic growth could be present. No one expressed any concerns about the potential threat of algae.