Candidates for Manhattan borough president agree: The city should prioritize making the East River safe and clean enough for people to swim in it. But the mayor hasn’t been so quick to jump in the water, and at least two other candidates for mayor voiced similar reservations, citing safety concerns as the primary reason to scrap the idea.

A Democratic candidate for borough president and member of the state Assembly, Adriano Espaillat, said a swimmable East River would boost tourism, enliven community spirit, and increase profits for waterfront businesses.

“It gives options for low-income families who can’t always take a whole day off and go out to Coney Island,” a spokesman for Mr. Espaillat, Joel Barkin, said. “As long as you can ensure it would be a safe swimming area, then it’s really a win-win situation for the borough.”

Another assemblyman and candidate for borough president, Keith Wright, watched his father swim across the East River on a dare in the 1950s, according to a spokesman, Basil Smikle.

“It should be something that anyone who would like [to do it] and is physically able should do,” Mr. Smikle said. “Mr. Wright himself has not done it, but he’s been wanting to.”

Most other candidates agreed with Messrs. Espaillat and Wright, but three candidates for mayor did not.

C. Virginia Fields, who is leaving her post as president of Manhattan to run for mayor, said in a statement that swimming in the East River is too dangerous, especially considering the risk of drowning incidents.

“I would not support any project that would encourage New Yorkers to put themselves unnecessarily in harm’s way,” Ms. Fields said. When told that a former Massachusetts governor, William Weld, jumped into Boston’s Charles River in 1996 to highlight his environmental improvements, Ms. Fields said: “It sounds like a great idea for Mike Bloomberg.”

Though Mayor Bloomberg has made cleaning up the waterfront a priority, he still has reservations about the East River’s treacherous conditions, according to his campaign spokesman, Stuart Loeser.

“He’s also cleaning up the water in the East River,” Mr. Loeser said. “But no matter how clean the water gets, there is still a strong current in the East River that makes swimming a dangerous prospect.”

One of Mr. Bloomberg’s most outspoken critics, Rep. Anthony Weiner, said he supports taking advantage of the city’s waterways but doubts the feasibility of an East River plan.

“I think we should strive to have all our waterways be as clean as possible, but I am not encouraging my constituents to jump in the East River anytime soon,” he said.

Eight candidates for Manhattan borough president said they supported creating a swimmable East River. The borough presidency is being sought by a large field of candidates who are all Democrats, save one: Barry Popik. He and Council Member Margarita Lopez were the only two candidates who said the idea had some merit, but the river still may not be safe for swimming.

One candidate, Carlos Manzano, said that as long as pollution and currents were not a problem, he would create a task force of engineers and advocates to assess the situation.

“When a feasible idea has been created, he would lobby the city and state to make it a reality. Carlos would LOVE to swim in the East River,” a spokesman for Mr. Manzano, Gregory Durham, said.

The East River’s water quality is often compromised after rainfall, which overflows treatment plants and causes sewage to pour out into the water. Another candidate, Brian Ellner, said he would aim to prevent that kind of pollution.

“We must … strike for infrastructure improvements to ensure that we can handle all overflow,” Mr. Ellner said.

City Council Member Eva Moskowitz, another Democratic candidate, said historical accounts of swimming in the East River around the turn of the century appealed to her.

“I think it would be great to return to those glory days,” Ms. Moskowitz said.

Stanley Michels, who served on the City Council for 24 years, said he liked the idea in theory, but in practice cleaning the river would be a challenge.

“The whole thing would probably take 50 years. It could be made swimmable, but it would take much work and much money,” he said.

Council Member William Perkins, another candidate, said the plan might not be “as costly as one might think,” and said along with Assemblyman Scott Stringer that they would use the Hudson River as a model, which Governor Pataki wants to make swimmable by 2009.