Frequently Asked Questions About Microcystis

What is Microcystis?

Microcystis is a variety of blue-green algae that typically appears as thick green scum on the surface of nutrient-rich bodies of water. The blue-green algae (Cyanobacteria) blooms are a natural phenomenon in nutrient-rich lakes, reservoirs, and slow moving bodies of water around the world.

Is Microcystis toxic?

Several species of blue-green algae, including Microcystis, are known to produce potent Hepatotoxins (liver toxins) that are called Microcystins.

Has Microcystis been found in the Sacramento/San Joaquin Delta?

Microcystis was first detected in the Delta in 1999, but the blooms in the Delta occur occasionally and have not grown severe enough to warrant a drinking water health warning from the U.S. Environmental Protection Agency.

Is it dangerous to drink treated Delta water?

Treated Delta water is perfectly safe to drink. Water agencies that treat and distribute water in systems that rely on the Delta have not been affected by Microcystis. The Contra Costa Water District (CCWD) gets 100% of its water from the Delta. CCWD monitors weekly all of its water sources for algae blooms. CCWD uses ozone for disinfection at its water treatment plants. Ozone effectively reduces Microcystin toxins to below detection levels.

Has CCWD found Microcystin in any of its reservoirs?

The results of past analyses indicate that occasionally there is some Microcystin being produced in Mallard and Los Vaqueros Reservoirs by Microcystis. However, levels at both locations did not exceed the World Health Organization’s guideline of 1.0 ug/L. Furthermore, CCWD can avoid bringing the algae into its system because water pipes in the reservoirs are located well below the surface where the algae can be present. No Microcystin has ever been detected in water leaving CCWD’s treatment plants.

Are there government regulations on Microcystis or Microcystin levels in the United States?

Currently, there are no U.S. regulations for these in drinking water. The World Health Organization has issued a drinking water guideline of <1.0 ug/L for Microcystin.

Should we be concerned about Microcystis in the future?

Scientists and health officials are studying the Delta to determine whether Microcystis is contributing to, or is a result of, the decline of fish populations in the Delta. Water districts that rely on the Delta as a source of drinking water are keeping a very careful watch on this issue. CCWD drinking water is monitored and tested continually and results are reported to customers every year in the Annual Water Quality Report. CCWD is a leader in the fight for state and federal funding for improvements in Delta water quality.