The West is known for summer wildfires. Now it seems Western summers will be distinguished by another kind of flare-up: algae blooms.

This summer has witnessed an explosion of algae problems in Western water bodies. Usually marked by a bright green mat of floating scum, the blooms are unsightly and unpleasant for water lovers. More concerning are potentially toxic cyanobacteria often produced by the algae, which can be deadly to pets and livestock and cause illnesses in people.

These harmful algal blooms have popped up in freshwater lakes and streams for years. But in recent years they seem bigger and more widespread than ever, resulting in closed beaches, public health warnings and risks to drinking water in a few locations.

Blooms are even popping up in unlikely places, such as high-elevation mountain lakes.

But there is currently no federal drinking water standard for algal toxins and in many places, data monitoring of blooms is still scarce.

“This is really a devilish problem,” said Craig Cox, a senior vice-president for agriculture and natural resources at the Environmental Working Group who is tracking the issue. “The more I look into it, the more stunning the state of play seems to me.”

While the cause of each incident is not always known, two of the main known drivers of algal blooms are excess nutrients in the water and extreme heat. As a result, algae-coated lakes could become one of the most visible consequences of rising global temperatures.

The most serious incident recently occurred in May in Salem, Oregon, where a health advisory was issued to more than 200,000 customers of the city water department following the detection of algal toxins in the drinking water supply. Young children, the elderly, pregnant women and people with certain medical conditions were warned not to drink tap water for most of the month of June.

Salem officials still don’t know what caused the toxic bloom.

“That’s the million-dollar question that everybody wants to know,” said Lacey Goeres-Priest, water quality supervisor at the Salem Public Works Department. “There’s a lot of different factors that play into this type of event.”

The algae and the bacteria involved in harmful blooms are all naturally occurring and are important building blocks of all life on Earth. But the two main causes of the blooms are not natural.

To learn more about algal blooms and what's causing them, click here to read more.