Richmond officials, after allowing swimmers to use the popular indoor pool at their own risk since 1997, abruptly shut the 76-year-old facility on Wednesday.

"I don't see where the city had much of a choice," said Bob Strauss, a member of Save the Plunge board and an occasional swimmer. "The pool does need work.

"We have been pushing for years to get engineers in there, but the city is moving at municipal speed -- somewhere between glacial and geologic."

The City Council finally heeded the call yesterday during a closed-door meeting at which it was decided to hire a structural engineer to examine the pool, considered the East Bay's equivalent of San Francisco's Sutro Baths.

"There's concern that trains rumbling by the building could trigger the framing to collapse," said Vice Mayor Nat Bates.

The safety of the city-run pool, adjacent to railroad tracks in Point Richmond, has been widely debated since the 1989 Loma Prieta earthquake. Plunge supporters persuaded the city in 1997 to allow swimming after voters rejected a $24 million bond issue that would have financed seismic repairs.

At that point, city officials erected "Swim at your own risk" signs.

The engineering firm selected by the council yesterday also examined the Plunge in 1997. Inspectors found ornamental stone falling from the east wall and fissures topping 10 feet long. Inside, reinforcing rods poked from the wall like exposed ribs, plaster crumbled like talc, and the western wall -- made of hollow clay brick -- sagged.

That wall is where Wednesday's mysterious bulge appeared.

This week's closing also has renewed the debate in Point Richmond over whether the landmark, built in 1925, should be razed or retrofitted.

Save the Plunge is ready to fight for a retrofit but will await the engineer's report before proceeding.

"Everybody who uses it is concerned, but if it's unsafe, the city has to close it and respond quickly," said Richard King, a member of the Save the Plunge trust.

The group has raised $151,000 to help restore the Plunge, a project that will cost between $5 million and $8 million. Save the Plunge worked with a videographer to make a documentary about the pool and held jazz concerts to raise money.

Councilman Tom Butt agreed that the city should have stepped in sooner.

"I've been saying for 10 years that regardless of any cracks, that building is deteriorating and we need to restore it."