Green pond scum floating on a lake is not just unsightly. As animal lovers have learned the hard way, it can be deadly. Here’s what you need to know to protect yourself and your pets from toxic algae blooms.

In recent days, three pet dogs in North Carolina and another in Georgia died after swimming in water contaminated with toxic organisms. Warm temperatures and an influx of nutrients from agricultural runoff or other sources can prompt toxic algae and bacteria to grow out of control. The result is a phenomenon called a toxic algae bloom. As the planet warms, these blooms are becoming more frequent — leading to a greater chance for human and animal exposure.