Des Moines Water Works has detected microcystin, a dangerous toxin from blue-green algae, in Des Moines tap water, but within federal limits. The toxin can damage people’s livers, gastrointestinal system and nervous system, and often kills pets and other animals at high levels. Scientists don’t fully understand what conditions lead blue-green algae — which are common throughout Iowa — to release the toxin, but Water Works chief Bill Stowe suggested farm runoff and the hot weather are likely to blame. The utility is checking for a variety of similar toxins. Typically, the treatment process should remove them. The elevated microcystin levels were found in water from the Raccoon River. The utility switched to water from the Des Moines River and adjusted treatment, and the water is safe to drink. There are no restrictions on using tap water from Des Moines Water Works.