In the wake of toxic algal blooms, how safe are California's rivers and lakes?

Reports of dogs dying after swimming in blue green algae-infested waters in California this summer have raised concerns about the health risks to humans who come into contact with the harmful algal blooms and the toxins they produce.

But in a state where there are no regulations to monitor the level of these dangerous toxins that, if ingested, can be fatal, how safe are our recreational water and drinking water supplies?

For my California Data Journalism Fellowship project, I plan to investigate the prevalence of blue green algae — or cyanobacteria — toxins in California lakes, reservoirs and rivers. Cyanobacteria, commonly known as blue green algae, are found in almost every kind of aquatic habitat.

In California, the problem has intensified during the drought because blue green algae thrive in dry conditions when lake levels are low and there is a lack of water turbulence.

While there are no known human deaths associated with blue green algae toxins, known as cyanotoxins, in the United States, 60 dialysis patients in Brazil died in 1996 due to the presence of the toxins in the water supply. And domestic poisonings and illness outbreaks are well-documented, according to the Centers for Disease Control and Prevention. The effects of chronic exposure to low levels of the toxins in drinking water are not known, but researchers and health officials have found that the toxins cause allergic reactions, skin irritation, gastrointestinal illnesses, joint pain, liver damage and, in some cases, cancer.

Still, the U.S. Environmental Protection Agency and Cal EPA do not require local agencies to monitor for cyanotoxins in recreational water bodies or drinking water supplies.

Since the 1990s, U.S. EPA has listed several cyanotoxins on three consecutive lists of contaminant candidates to regulate in drinking water. This past summer, the agency finally issued non-regulatory drinking water health advisory levels for two cyanotoxins.

The recommended limits for young children are 0.3 micrograms per liter for microcystin, a liver toxin, and 0.7 micrograms per liter for cylindrospermopsin, another liver toxin. For everyone else the thresholds are 1.6 micrograms for microcystin and 3 micrograms for cylindrospermopsin.

Because these standards are not mandated, it is unclear whether water agencies in California will adopt the guidelines and begin routinely testing for cyanotoxins in treated water supplies.

Although previous research has shown that water treatment processes are generally effective at eliminating the toxins, unsafe levels of microcystin have been detected in states that require testing. Last September, the City of Toledo detected dangerous levels of the toxin – more than 1 microgram per liter – at one of its water plants, prompting a three-day water shut off for about 500,000 people. Because of the toxin, the water was not safe to drink or even shower in, forcing residents to rely on bottled water shipped into the area.

Could the same happen in California? Let's find out.