Minutes after the 5-year-old yellow Lab got to the shoreline of Prairie Lake, he vomited.

Then he fell over and couldn't get up, said the dog's owner, Kirsten Tatge of Clear Lake, Minn. Shortly after being taken to the veterinarian, Copper the Lab died.

Although the cause hasn't been confirmed, Tatge's veterinarian suspects the dog ingested toxic blue-green algae that was in the lake.

The Minnesota Pollution Control Agency on Thursday advised keeping pets away from lakes, ponds and slow-moving streams covered in blue-green algae blooms. The blooms often look like green paint, pea soup or floating mats of scum.

Although not all blue-green algae is poisonous, MPCA officials say it's difficult to visually identify the toxic algae, which can be deadly to dogs, livestock and other animals within hours.

Animals may end up ingesting the toxins if they drink the water or lick their coats after emerging from the water.

Blue-green algae blooms can occur anytime during the summer but more often are associated with warm weather and low rainfall. When waterways develop high levels of nutrients, algae blooms.

"This year's unusually heavy rainfall has carried tremendous amounts of nutrients into Minnesota lakes," said MPCA scientist Steve Heiskary. "If the rain slows down and we move into a period of hot, dry summer weather, we could see an exceptional number of algae blooms across the state in the coming weeks, even in lakes that do not normally experience them."

State officials say animals that enter water with heavy algae growth should be hosed off immediately before they have a chance to lick themselves clean. Owners concerned their pets have been exposed to blue-green algae should immediately take their pet to a veterinarian.

The toxins can damage an animal's liver and cause neurological problems, said Elk River veterinarian Dennis Gallenberg. Although the toxic blue-green algae is a concern, he said he hasn't personally treated a dog that's been sickened by it.

For humans, toxic blue-green algae can cause nausea and skin, eye, nose and throat irritation. MPCA officials say human deaths from exposure to blue-green algae are rare because the unpleasant odor and appearance of blooming with algae is often enough to keep people out of the water.

Tatge said she and her family, including four children and three dogs, spend many summer days in Prairie Lake, which is outside their back door. On Sunday, friends, family and two of the family's three dogs were playing in and around the water with Copper fetching tennis balls from the lake.

"My husband saw him come out of the water, stagger and fall over," Tatge said. "He couldn't get up. … He was fading fast.

"It happened so quickly," she said. "That's what was so shocking."

Mary Lynn Smith • 612-673-4788