The first major outbreaks of blue-green algae were spotted in Horse Creek Cove, Bernice State Park and Duck Creek. Officials said Friday the algae now has spread to most parts of the lake. Coves have been conducive to the algae’s growth because of calm water. High temperatures, coupled with the elevated presence of nitrogen and phosphorous in the water, also have helped fuel algae growth. Graphic by Tulsa World

The Grand River Dam Authority on Friday strongly cautioned people to stay out of Grand Lake because of blooms of potentially dangerous blue-green algae, which can cause intestinal and respiratory problems in humans and animals if ingested in large enough amounts. The following are some questions and answers about the situation:

What is blue-green algae?
A free-floating microscopic organism that is naturally present in lakes but usually found in low numbers. It is actually cyanobacteria. It is dangerous because of its ability to produce and release toxins in the water.

When will it be safe to go back in the lake?
Officials said Friday it’s unclear when it will be safe. Algae blooms can persist for weeks or even months.

How do I know whether I’ve been affected?
The toxins can cause stomach and intestinal illness, trouble breathing, allergic responses, skin irritation, tingling fingers or toes and, rarely, liver damage. Children are particularly susceptible.

If I’ve been in the lake in the last week or two, what should I do?
Symptoms cannot be prevented after contact, but those who develop severe symptoms should contact their physician. Some symptoms can develop within minutes, but others can take a week to appear.

What should I do if I come into contact with blue-green algae?
Wash with fresh water and soap after skin contact.

Should I eat fish caught in a lake with blue-green algae?
Although the danger of eating fish from water with the algae isn’t completely understood, health officials do not recommend it.

How did this happen?
The algae uses oxygen and photosynthesis to reproduce. It feeds on phosphorus and nitrogen that can come from lawn fertilizer, chicken litter or sewage treatment runoff. Officials said Friday the lake had elevated levels of phosphorus and nitrogen. The algae grows mostly in hot temperatures and still waters. Recent high temperatures helped fuel that growth.

Is there anything that can be done to get the algae out of the lake?
Nothing feasible. Until it expends its primary fuel sources — oxygen, nitrogen and phosophorous — it will continue to survive. Chemicals can kill the algae, but the amount of chemical needed would create a different set of environmental and health concerns.

What do blue-green algae look like?
It can have a green, bluish, brownish or reddish-green color and has the thickness of soup or paint. It can look like an oil slick. On the shore, it can form a thick mat

Sources: University of Tulsa biology professor Mark Buchheim; Oklahoma State University botany professor Bill Henley; Lauri Smithee, chief of acute diseases at the Oklahoma State Department of Health; the Oklahoma Department of Environmental Quality and the Centers for Disease Control.

— By Shannon Muchmore and Randy Krehbiel, World staff writers
Watch a slideshow of how visitors spent their weekends at Grand Lake.
tulsaworld.com/photos

Get more information on blue-green algae.

June 24: The Oklahoma Department of Environmental Quality issues a warning for people to stay away from Bernice State Park on Grand Lake because of blue-green algae.

June 27: Sen. Jim Inhofe swims in Grand Lake near Ketchum. He later says he was "deathly sick" after the swim.

July 1: The Grand River Damn Authority has an emergency meeting to discuss the blue-green algae outbreak and possible implications on the lake for Fourth of July weekend. During the meeting,it was shown that some toxins in Grand Lake exceeded international standards by as much as 18-fold. The GRDA took no official action on the outbreak, but warned against bodily contact with the water, especially shallow areas.

July 2: The World interviews Gov. Mary Fallin, who was vacationing on Grand Lake. Fallin had previously urged tourists to come to the lake for its other amenities. A fireworks at Bernice State Park is held as scheduled.

July 3: A fireworks show at Duck Creek is held.

July 5: DEQ officials say they will continue daily testing of the Grand Lake waters for blue-green algae into the foreseeable future.