When it rains, mats of tangled trash and debris -- some with tentacles 50 feet long and 3 feet thick -- flow down the flood-control channels and foul the marinas. The snarls of urban flotsam are flecked with plastic bottles, Styrofoam and other castoffs.
Water quality plunges as pesticide, chemical and bacteria counts rise. Errant boaters sometimes illegally dump their raw sewage into the harbor. And the silt pours in and settles to the bottom of the waterways, making them shallower.
This isn't the heavily industrialized Port of Los Angeles. It's affluent Huntington Harbour in Orange County, a Venice-style enclave of million-dollar homes, 3,500 pleasure boats and inviting pocket beaches tucked along the quiet back channels of Anaheim Bay.
Carved from wetlands four decades ago, Huntington Harbour has long been a symbol of the good life. There's a yacht club, a Christmas boat tour of decorated estates, and waterfront restaurants and boutiques along the main channel.
But serious environmental problems are threatening the community's quality of life, and years of unchecked silt deposits have left some places so shallow that boats sit in the mud or cannot pass at low tide.
"Trash, debris, pesticides and toxic metals get dumped into flood control channels," said Ken Theisen, a staff scientist with the Santa Ana Regional Water Quality Control Board. "What has happened in Huntington Harbour can happen in any urban watershed. It doesn't matter how much money you make."
Huntington Harbour's residential islands contain about 5,000 residences, some of them luxury compounds that go for as much as $4.5 million and come with a slip for the family yacht.
During warm weather, the harbor's canals and secluded beaches fill with swimmers and kayakers, many of them children. Flotillas of small sailboats and other craft bob in the main channels with larger sailboats and motor yachts.
Those who work and live in the harbor say they worry about encroaching pollution, the flows of debris in winter, and the silt that is slowly filling the channels.
"Most of the time, the water quality isn't that bad," said Clement Aime, who lives in a waterfront condominium with a slip for his cabin cruiser. "But residents don't want the harbor going to hell. They don't want the water polluted."
Although the harbor's channels and beaches have good water quality most of the year, testing shows that is not true after moderate-to-heavy storms, particularly in the fall and winter.
The degradation occurs as polluted urban runoff, much of it from upstream cities, gushes into the harbor through hundreds of storm drains and three major flood-control channels -- the Bolsa Chica, the Sunset and the East Garden Grove-Wintersberg channels.
The watershed that drains into the harbor is enormous and includes Disneyland's parking lots far upstream.
Once in the canals and main channel, polluted water and debris become trapped in a harbor that lacks the surf and ocean currents needed to flush out the runoff.
"Enclosed beaches and waterways are the worst performers in terms of water quality," said Mitzy Taggart, a staff scientist with Heal the Bay, a Santa Monica-based environmental group.
County health department records show that in 2000, 2001 and 2002, contamination warnings were posted at Huntington Harbour more often than for most of Orange County's coastal waters. Only Huntington State Beach, Newport Bay, Dana Point Harbor, Doheny State Beach and Poche Beach in South County had more official warnings.
Last month, the federal government added the harbor to its list of impaired bodies of water after the Environmental Protection Agency found unacceptable levels of polychlorinated biphenyls, better known as PCBs, and dieldrin, a pesticide similar to DDT, that was banned in 1973.
PCBs, which remain in the environment for decades, are organic compounds once used to make electrical equipment, paints, plastics and rubber products. Studies show they can affect brain development in human infants as well as the immune and reproductive systems of larger marine animals.
The extent of the harbor's water pollution still isn't known. State water quality officials and Orange County Coastkeeper, a local environmental group, are developing a comprehensive survey of the area. The findings, based on 90 water and bottom samples taken in March, haven't been released.
Coastkeeper maintains a 22-foot power boat in the harbor to help monitor water quality. This month, executive director Garry Brown stopped the craft near the Warner Avenue bridge, where runoff flows in from the Wintersberg Channel. He recalled that a bottom sample taken here in March emerged from the water as putrid black goo molded around a large amount of trash.
"When we pulled it up," Brown said. "Everyone grabbed their noses."
Pollution is only part of what arrives with the urban runoff. The flow also brings in silt, which slowly fills the channels and canals.
A 2000 survey of the harbor identified 10 sites that needed immediate dredging.