More than 375,000 gallons of sewage have spilled into the Ala Wai canal the past two days while city crews, hampered by heavy rains, work around the clock to try to stop the flow.

The crews were expected to work through the night last night.

Late yesterday afternoon, a diver was brought in to assess the situation, and discovered that a 42-inch sewer main on Kai'olu Street, just makai of the canal, was cracked.

At about 9 p.m. yesterday, crews were working to expose more of the main to determine which parts remained sound.

Signs warning of water contamination were posted Friday and yesterday along the canal and at Ala Moana Bowls, a surf spot near the Ala Wai's mouth.

The problem began when the sewer main failed early Friday morning. The untreated wastewater ran into a storm drainage system that leads into the canal.

Because the storm sewer was overwhelmed with water, the crews, working in a murky swimming pool as they dug for the main and fearful of a sewage-laden flood as the rains continued to fall, made further releases of the wastewater into the Ala Wai.

"We need to expose the main before repair can begin," Eric Takamura, director of the city Department of Environmental Services, said in a statement yesterday afternoon.

The problem was complicated by other underground utilities near the main, he said. The main feeds into the Beachwalk Wastewater Pumping Station.

Among the victims of Hawai'i's most recent flooding event were 20,000 rubber duckies that ran afoul of the sewage yesterday afternoon during the 19th annual Great Hawaiian Rubber Duckie Race in the Ala Wai canal.

"The water was high and brown but the ducks were clean and new, so they were really shiny," said Janice Suzuki, one of the volunteers who scooped the bathtub toys out of the canal at the end of the race, a benefit for the United Cerebral Palsy Association of Hawai'i.

Although city officials said workers patrolling the Ala Wai warned users of the spill and United Cerebral Palsy had been notified, Suzuki said she was unaware the Ala Wai had been additionally fouled.

"It actually looked cleaner than it has in the past," she said. "There was only one dead fish."

The volunteers, members of the Rising Phoenix chapter of the Junior Chamber of Commerce, were provided with alcohol wipes and latex gloves this year, said Craig Matsuda, who coordinated the duck catch.

"We'll be fine," Matsuda said. "We're a hardy group."

Reach Karen Blakeman at kblakeman@honoluluadvertiser.com.