A number of Minnesota cities have reported blue-green algae blooms this summer, causing the temporary closing of some beaches. Blue-green algae is bacteria that can be toxic for both humans and pets.

"We have a lot packed into this park so on a typical summer day it's busy from one end to the other," said Amy Markle, Parks and Recreation Director for Eden Prairie.

For about a week and a half, Riley Lake Beach in Eden Prairie was shut down after the detection of blue-green algae. Water samples confirmed that the bright green bloom with blue streaks, which looked like spilled paint, contained harmful toxins.

"The tricky thing with blue-green algae is sometimes, when the bacteria break down, that's actually when the toxins can be released," said Markle.

If ingested, the bacteria can cause vomiting, diarrhea, rash and headache. Blooms have been found earlier than normal this year, due to early ice-outs on many lakes.

Algae blooms are fueled by two things: an abundance of nutrients in a lake and rapidly warming water temperatures.

"Think about a garden, and you need sunlight and water and nutrients in a garden. And you are going to have a great, beautiful garden. Well, algae is a lot of the same way," Kim Laing, with the Minnesota Pollution Control Agency, said.

Laing said the only real preventative measure is to keep nitrogen and phosphorus from getting into lakes and ponds.

"Whether it's vegetative buffers, or other avenues, try and keep those nutrients on the land and out of the water," said Laing.

As for Riley Lake Beach, it re-opened after 10 days. Swimming has returned, but with hot days ahead, they'll continue to keep a close eye on the water.

"It's kind of the perfect recipe for it, so our lifeguard team is watchful. They do a visual inspection in the morning to see if there is any present before we open the beach up for swimming," said Markle.

The Environmental Protection Agency on how you can detect and report an algae bloom, if you see one in your area.

• Algae Bloom