This weekend, 1,500 athletes from across the country and the world will plunge into the frigid ocean off Lovers Point to compete in a 1.5-kilometer swim, the first leg of the Seagate Triathlon in Pacific Grove. The swimmers will brave 58-degree water, a fierce current, a tangle of kelp, and quite possibly a swell of waves threatening to crash them against the craggy shoreline. But that may be the least of their worries. They may also have to battle an onslaught of microscopic assailants--fecal coliform bacteria.

Personal trainer Jennifer King makes a living by teaching people to lead healthy lives. So when three of the 18 athletes she''s coaching for the triathlon came down with earaches, sinus infections and diarrhea, she wasn''t at all happy about it. Though none of King''s trainees consulted physicians, the triathletes think their infirmities are the result of training in the waters off Lovers Point, where twice this year--in January and August--raw sewage has spewed from stormwater outfalls into Monterey Bay. Indeed, the athletes'' symptoms are similar to those associated with exposure to unsafe levels of fecal coliform, which can cause ear infections and diarrhea, among other illnesses.

This year''s two big sewer spills off Lovers Point prompted the Monterey County Health Department to close the beach. Five more times this year, including last week, the health department posted signs at Lovers Point warning swimmers of a high bacteria count in the water.

It''s an unpleasant surprise to people who think of Monterey''s waters as clean and safe. "I don''t get it," King says with disgust. "I thought this was a marine sanctuary."

Among those athletes braving the murky waters this weekend will be Monterey resident Alan DeVilliers, who has trained for the race for the past three months by swimming off Lovers Point and Del Monte beaches. This summer, he''s suffered from an ear infection, a nasal infection, nausea and other ills not normally discussed in polite company (he''s "not been able to have a solid stool for a while"). A friend of his who also swims in the bay has suffered from an intestinal infection. "I think there''s something correlated with people getting ill and something in the water," he speculates.

Local triathletes aren''t the only ones who believe they''re getting sick from dirty ocean water. A.J. Jordan, a representative of the local chapter of the Surfrider Foundation, says he''s received several calls this year from surfers concerned about water quality. "I do know people who have gotten sick and they did wonder whether it was from the ocean," he says. "I have had people calling me wondering whether the water is safe, because they''re worried."

As an organization dedicated to preserving clean ocean water, Surfrider Foundation runs a coliform testing program in Santa Cruz and other beachside communities, but there is no such program on the Peninsula--yet. As a result of increased concern over water quality, particularly in Pacific Grove, Jordan says the foundation will start testing locally this winter. "We have a reason to believe there is a need for independent testing," he says. The group will also begin gauging the health of surfers this week by asking them to fill out surveys at On the Beach and Sunshine Freestyle surf shops.

It Runs Downhill

Pacific Grove''s chronic sewage spill problem undoubtedly adds to contamination in the bay--there''ve been four spills in the last two years, including a colossal 70,000-gallon spill in January that cost the city $70,000 in state fines. P.G.''s sewage spills are believed to be caused by sewer lines clogged by either grease or organic debris, such as roots and branches. When a clogged sewer line backs up, sewage overflows into the city''s storm drains, which flow to the bay. The city has stepped up sewer cleaning efforts as well as the enforcement of an ordinance requiring restaurants to install grease traps.

However, P.G. alone is not to blame. A sewage spill closed Spanish Bay Beach earlier this year. And since January 1, 14 warning signs have popped up on a number of other Monterey beaches: Del Monte, San Carlos, Asilomar, Spanish Bay, Stillwater Cove and Carmel beaches. In 1999, nine such warning signs were posted on area beaches.

Beyond sewage spills, the culprit is most likely urban runoff, says Walter Wong, county environmental health director. Throughout the Monterey Peninsula, any liquid that makes its way to a street storm drain ends up in the bay. Fertilizer runoff from lawns and farmland mixed with cat, dog and bird feces containing coliform bacteria is a potent mixture that causes ocean water contamination. "Once you have coliform, you know you are getting waste material from the intestines of either humans, animals or insects," Wong says.

The current plunge in water quality seems to be a recent phenomenon. DeVilliers says that he trained the same way for the triathlon in 1997 and that he has surfed the area for years without health problems. And Jordan says calls from sick surfers started earlier this year. Indeed, the number of beach warnings and closures has swelled this year, but health officials are cloudy on what is causing the upsurge in contamination. "We''ve had more postings this year than last, and prior to 1999, we had hardly any postings," Wong says.

However, Wong says that increased regulation, not increased bacteria levels, may have something to do with the rise in reported contamination. As of last year, state law requires weekly testing of ocean water April through October and lowers the threshold for warnings and beach closures. Prior to the new law''s effect date, local beaches were tested just once a month.

Not exactly a comforting explanation, but there it is. At least the water still looks nice.