Honolulu Community College's Marine Education and Training Program, whose facility fronts the lagoon.

"They are widespread throughout this area. They are clearly very abundant," Crow said. "I feel pretty confident that that's what's stinging people."

Ke'ehi's water was murky yesterday, and although it was a hot day, no one was swimming. Paddlers have been complaining for several weeks that those swimming at Ke'ehi or holding canoes before the start of races have been suffering painful bites or stings.

Kane'ohe Canoe Club paddler Eric Moncriffe said he was severely stung at Ke'ehi two weeks ago and sought treatment at a hospital.

O'ahu's canoe racing federations are making plans to move regattas to other locations until the stinging stops. Hui Wa'a canceled its regatta last Saturday and is moving this weekend's event to Ma'ili, said its permitting representative, Rebel Chamizo.

O'ahu Hawaiian Canoe Racing Association president Hannah Anderson said her organization also is exploring alternate locations.

"There could be 30, 40, 50 people in the water at one time. What if one of them is allergic to the sting?" Anderson said. "We can't risk that."

She said the state Department of Health was informed months ago that there was a problem, and she hopes the state can do something about it.

Health Department Clean Water Branch official Watson Okubo said the department's new plankton net arrived yesterday and his staff anticipated doing its own collections at Ke'ehi this morning.

Okubo said some of the descriptions by afflicted canoe paddlers suggest to him there may be another marine organism, or multiple organisms, involved. He said there were cases of people being stung through their wetsuits and others stung where their swimsuits rubbed against their skin.

Okubo said that aku fishermen have long been aware of the possibility of being stung at Ke'ehi. Okubo said his grandfather would enter the bay with an aku boat crew to catch bait for fishing, and someone always had to jump into the water to close the net.

"They got itchy, too," Okubo said.

Crow said stinging hydromedusae has been reported in Hawai'i for many years, at least since the 1950s, although the creatures appear to go through population cycles. In other parts of the world, populations of similar creatures can rise in the spring and summer months and remain present in large numbers for three to four months, he said.

Crow said he consulted with University of Hawai'i marine scientists Susan Brown and Cindy Hunter, and Waikiki Aquarium jellyfish expert Mike Callahan. He went to the site yesterday with Hawai'i Institute of Marine Biology's Darren Oshiro, whose kids paddle canoes. Oshiro said getting stung while swimming in paddling areas is not that uncommon.

"From what I understand from talking to the coaches and the paddlers, they get hit all over the place" and not just at Ke'ehi, although the Ke'ehi stinging appears to have been unusually severe, Oshiro said.

Brown, who took samples in the lagoon Friday, said the animals are "just about microscopic." The jellyfish's bell is clear and 0.5 millimeter to 1.5 millimeters thick — about the size of the ball at the end of a ballpoint pen. The tentacles are two or three times as long as its body.

Hunter, a coral reef ecologist, said she suffered a minor sting on her foot while taking samples yesterday. She took them back to her laboratory for study.

"I kept my eyes open for anything that could have done it. This was the only candidate I could find," she said.

Crow said he is still trying to establish the precise species of the Ke'ehi creatures.

He said hydromedusae have a complex life cycle. During one part of their lives they are polyps that remain affixed to the ocean floor, and perhaps to mangrove tree roots and dock pilings.

The free-floating tiny jellies "bud" off the polyps and are released into coastal areas, where they feed by using their stinging tentacles to paralyze tiny marine crustaceans.

The jellies are male or female and reproduce sexually to form drifting planktonic forms. These eventually settle to become new polyps.