KAILUA — An algae bloom is spreading over Ka'elepulu Pond, robbing it of oxygen and causing a fish kill, according to a marine biologist who is a resident of the Enchanted Lake subdivision.

Marine biologist Bob Bourke, who works for local high-tech firm Oceanit, said he saw many dead fish in the pond yesterday. Bourke said runoff of fertilizers in the area has caused the algae to bloom, and that, combined with stagnant water, is robbing the 80-acre pond of oxygen.

Bourke said that yesterday he saw dead fish of various species including "thousands of native gobie."

Residents have complained that the problem is caused by the city not opening the mouth to Ka'elepulu Stream regularly, but officials earlier this week said the work is done monthly. Unfortunately the stream mouth can close again soon after it is opened, said Larry Leopardi, chief of the city's Road Maintenance Division.

"Once we open the stream, it may close the very next day because of the currents and shifting sand," Leopardi said, adding that the city is doing what it can. "But if the expectation is for the city to be out on a daily basis, I don't have the resources for that."

Environmental problems are not new to the area. The pond has had problems with odor, silting, invasive plants and unwanted birds.

On Nov. 13 residents called the state Department of Health to inspect what they thought might be a possible oily paint spill. But Michael Cripps, with the Hazard Evaluation and Emergency Response unit, said he determined that some kind of algae bloom was taking place.

Bourke said the algae bloom leads to a fish kill under certain conditions. The algae create oxygen during the day, and on sunny days a lot of oxygen is produced, he said.

On overcast days however, the algae don't create enough oxygen for the pond. During the night there isn't enough oxygen for the plants and the fish, and that causes a fish kill, he said.

The solution is to open up the mouth of the stream and let the pond flush, Bourke said. Although the city said it opened the stream three times in the last three months, not much flushing has occurred, he said.

"So I'm trying to figure out how to get someone to open the lake and let it breathe a little," Bourke said.

Reach Eloise Aguiar at eaguiar@honoluluadvertiser.com.