Lake County health officials are warning people to beware of blue-green algae following the death of a dog that had been frolicking in Clear Lake last week.

The dog became severely ill and was euthanized after its family visited Konocti Bay, where the dog had played fetch in the water, said Lake County Public Health Officer Dr. Karen Tait.

She's submitted samples of the dog's tissue to the California Animal Health and Food Safety Laboratory in Davis in an effort of determine whether toxins that can be produced by some types of decaying algae caused the dog's death. Results are expected next week.

When ingested, blue-green algae can produce toxins that cause a range of health problems, including liver failure, Tait said. The dog had symptoms that included vomiting, diarrhea and lethargy, she said. The algae also can cause rashes on contact.

Tait does not know of a previous cases of canine deaths from ingesting algae toxins in Clear Lake but occurrences have been reported across the nation.

State health officials in 2009 reported several possible cases in Northern California, including some related to the Eel River. At the time, they reported there had been 11 cases of dog deaths following contact with fresh water in Mendocino and Humboldt counties since 2001.

Tait said only tests can confirm the cause of the dog's death.

Other dog owners living along Konocti Bay have reported no ill effects from allowing their pets in the water, Tait said.

Tests can determine whether algae is producing high levels of toxins, but the results are not immediate and the tests are costly. The best precaution is to avoid swimming in areas that are thick with algae, Tait said.

"When you see it, stay out of it," she said.