Some residents of Kailua’s Enchanted Lake neighborhood worry that growing mats of alien algae covering parts of Kaelepulu Pond may soon cause a big stink in what is their backyard.

Bob Bourke, a resident and environmental scientist, believes conditions are ripe for an algae bloom so large it could suffocate the pond’s fish, killing off everything else in it.

"There’s so much algae that it pulls the oxygen out of the water," he said. "We will end up with tons of algae and dead fish."

The community’s problem with its privately owned, 100-acre pond may quickly develop into a broader public concern "if the whole lake goes septic and drains out into Kailua Beach," said Bourke, vice president of the Enchanted Lake Residents Association.

Bourke says while algae blooms appear every spring, the volume this year is "10 times greater than we’ve ever seen before." He estimates that there are 500 cubic yards of algae in the pond — equivalent, he said, to 50 dump truck loads.

He said he believes muddy runoff from a nearby hillside construction project is causing the robust algal bloom, and that a lack of fresh seawater circulating in the pond has exacerbated the problem. No seawater has entered the area since September when the city stopped dredging the mouth of Kaelepulu Stream, which winds its way from the pond to Kailua Beach.

The Enchanted Lake Residents Association wrote letters to Delta Construction, which is nearing completion of 10 residential lots on the hillside near the pond, complaining of sediment-filled runoff, which adds nutrients to the water and causes the algae to bloom and proliferate, according to Bourke.

Delta has not returned repeated calls over the past week from the Star-Advertiser.

The algae problem "is more than a small community can deal with," Bourke said of the association, which represents owners of 140 houses and 110 townhouse units.

Members of the association filed a complaint with the state Department of Health regarding the runoff.

State Deputy Health Director Gary Gill said the department has received complaints concerning the construction project. Health workers have inspected it and the company has installed best management practices, but the investigation and a enforcement case regarding polluted (soil) runoff is pending, he said.

Bourke identifies the ogo-like algae as Gracilaria tikvahiae, which was brought to Hawaii by the University of Hawaii for mariculture use to provide an alternative to the dwindling native seaweeds. The algae rises to the surface beginning at midday and through the afternoon, he said.

Resident Rod Castanha, who has lived on the "lake" since 1968, said: "It’s usually on the side of the banks. … Now there’s islands of algae blooms. It looks like a golf course."

Bourke said he believes a 2,000-foot-long sprawl of algae, some portions as wide as 20 feet, on the side of the pond near the construction is an indicator the developer is to blame.

Gill said the pond has periodically gone anaerobic, causing a large fish kill, a half-dozen times in the past 50 years.

"The potential is always there," he said. "Kaelepulu Pond is a time bomb waiting for an anaerobic implosion.

"It isn’t necessarily triggered by a single construction project," he said, adding that animal waste, fertilizers, and everything else that washes from the streets into storm drains go into the pond.

Gill said heavy rain typically leads to a sizable nutrient input into the shallow pond. Nutrients stimulate algae growth, which goes through a life cycle. Microbes dine on dead algae, consuming the oxygen, and fish die, he said.

Gill said possible ways to alleviate the problem are to expand the wetland, which was six to seven times larger in the 1940s, or to dredge it.

Several small, dead fish were seen floating among the algae in a visit to the pond May 20.

But the 100-acre pond is teeming with life, including fish such as awa, lae, barricuda, mullet, as well as oysters, seahorses and water birds including the native Hawaiian coot and the native Hawaiian stilt.

The city Department of Facility Maintenance said it halted monthly sand plug clearing of the Kaelepulu Stream mouth after receiving a Sept. 21 U.S. Army Corps of Engineers letter, which the city says ended the authorization for stream mouth operations.

"The monthly stream mouth opening previously performed by the city helped reduce the monthly sand buildup from the channel area in case of emergencies and also released water from the Kaelepulu Stream that promoted intermixing of the coastal water to alleviate the stagnant condition of Kaelepulu Stream and Enchanted Lake," the city said in a written response to Star-Advertiser questions. "The reduced stagnant water condition helped minimize the algae blooms."

The city blamed the Army Corps for allowing a general permit for stream mouth clearing to expire in 2001, but that the city had been doing the monthly clearing by mutual consent until receipt of the Sept. 21 letter.

In response, the Corps stated it "is not prohibiting any situation the city deems necessary to protect public health or public safety."

The city said it is waiting for the Corps’ approval of an individual application that would allow use of an excavator on a monthly basis to clear the sand.

The Corps said it did not find any application for a renewal of a general permit, and could not say when the city’s application for a permit for the stream mouth clearing would be granted.