Keeping Pets—and People—Safe from Toxic Algae

Visible green slime in Lake Needwood during harmful algal bloom outbreak in September 2012.

By Patty Scott

Two years ago, our family planned to take our Yellow Labrador puppy Fiona to Lake Needwood near our home in Rockville, Maryland for a swim. Our puppy needed somewhere to exercise and the scenic lake near Rock Creek Park seemed like the perfect place. My husband, however, mentioned something about a warning for a harmful algal bloom. At the time, I had just started working on EPA’s National Lakes Assessment, the agency’s report card on the condition of the nation’s lakes, and thankfully knew about the dangers of harmful algal blooms. Blue-green algae can produce harmful toxins that can be fatal if ingested. Since people are not allowed to swim in Lake Needwood, the dangers are not as great for humans. However, dogs are especially at risk if they swim in or drink the water. We decided against taking Fiona anywhere near the lake.

While Montgomery County did not know the cause of the outbreaks in Lake Needwood, harmful algal blooms are often triggered by excessive levels of the nutrients nitrogen and phosphorus. Many of our lakes, rivers, streams and bays are becoming overloaded with nutrients from a wide range of sources. Excess nutrients spur the growth of algae to the point where they can explode into vast — and sometimes toxic — colonies of slime. Algal blooms often peak during the summer months, but in some parts of the country they occur year round.

Nutrient pollution is a growing concern because it threatens public health, recreation and our economy. National data is not easy to find on impacts to our four-legged friends, but sadly dog deaths have been reported due to harmful algae.

Warning sign advising residents and their pets to avoid direct contact with the water at Lake Needwood in Montgomery County, Maryland.

Like many pet owners, we treat Fiona and Jake, our other lab, like part of our family, and we’d be devastated to lose them. It’s best to keep pets away from the water anytime there is visible surface scum, if the water is discolored or if there is a strong musty smell. Also, keep in mind that not all waters are monitored. You can check EPA’s new How’s My Waterway app to find out about the condition of your local waterway and whether it’s been tested.

Everyone can help make a difference. One easy way to combat algae is to take care not to over-fertilize. And always remember to pick up pet waste. To learn more about how you can prevent nutrient pollution, visit

About the author: Patty Scott works in EPA’s Office of Wetlands, Oceans and Watersheds on communications and outreach.  She loves fishing, kayaking, cycling and other outdoor pursuits.