The North Baltimore Aquatic Club reported the coach, who was not identified, to swimming authorities in October 2011, according to USA Swimming, the Colorado-based governing body.
The coach was forced out of the position within 48 hours after club officials became aware of the allegation last fall, and the club contacted Baltimore County authorities, a source with knowledge of the situation said.
USA Swimming said it first received information about the alleged 1975 incident in August 2010, when a woman described the incident in a voice mail message. But the alleged victim did not follow up with an investigator.
Steven A. Allen, a Towson-based lawyer for the North Baltimore Aquatic Club, said he would not comment about former or present employees or coaches for privacy reasons.
"We follow the guidelines of USA Swimming, and we follow all legal guidelines," Allen said. "We are always vigilant to behavior that may be inappropriate in order to detect it or prevent it. It's our goal that a safe environment be provided, and we do everything we can do to ensure that there is a safe environment."
It was unclear whether any charges have been filed in the alleged incident.
As of Friday, USA Swimming had banned nearly 70 individuals, including coaches, from the sport over issues including sexual misconduct.
Rick Curl of Maryland, founder of Washington's pre-eminent swim club, was banned in September after allegations surfaced of a sexual relationship he had in the 1980s with a swimmer when she was 13 and he was 33, according to news reports. He voluntarily gave up his USA Swimming membership and waived his right to a hearing, according USA Swimming.
In 1989, Curl agreed to pay the family of his victim $150,000 over 11 years for "pain and suffering" as part of a nondisclosure agreement, The Washington Post reported. She did not press charges, per the agreement, according to the newspaper.
No other Maryland coaches appear on the list of banned individuals.
Jonathan Little, an Indianapolis-based attorney who has represented victims in cases involving USA Swimming coaches, said a culture of abuse has existed in American swim clubs for decades because officials have failed to act aggressively.
"Swimming needs to have an independent review [of] all claims of sexual misconduct because the leadership of swimming has proven that they are incapable of handling complaints about athlete sexual abuse," Little said Friday.
Phelps and his coach, Bob Bowman, took over the North Baltimore Aquatic Club and the Meadowbrook Aquatic Center after the 2008 Beijing Olympics. Efforts on Friday to reach Phelps and Bowman were unsuccessful.
In recent years, USA Swimming has enacted new policies to confront a growing chorus of allegations of coaches sexually abusing underage swimmers. The reforms include enhanced criminal background checks of coaches, officials and volunteers and mandatory reporting of any inappropriate conduct.
The organization provided to The Baltimore Sun a copy of an email to "parents and friends" that addresses the local allegation. The organization also said it had notified Baltimore County police of the allegation.
"We believe strongly in our responsibility to provide responsible communication on this issue," the organization wrote in the email.
The alleged incident occurred while swimming was governed by the Amateur Athletic Union; USA Swimming, and its code of conduct, were not in existence until 1979, according to Karen Linhart, spokeswoman for the organization. For that reason, USA Swimming said, it could not enforce a violation of any rules.
After the organization received the anonymous voice mail in August 2010, an official returned the call and spoke to the alleged victim, Linhart said. The person provided details of the alleged incident but did not name the coach or give USA Swimming her name, she said.
"Despite not having the coach's name, USA Swimming attempted to initiate an investigation into the conduct described by the unidentified woman," Linhart wrote in an email. "However, our investigator made multiple attempts to contact her which proved unsuccessful over a period of three months."
The organization reported the incident to Baltimore County police. "It is our policy to report any information regarding the sexual abuse of a minor to local authorities," USA Swimming said.
"Because child sexual abuse is a criminal act, we feel it is most important that it is referred to the police."
About a year later, the Baltimore club relayed information to the oversight group about an alleged "inappropriate act by a coach," Linhart said.
Linhart said efforts by USA Swimming to prevent and respond to abuse include policies and guidelines, screenings, training, monitoring and supervision, reporting and feedback. The organization's highest penalty is a lifetime ban. Complaints that involve abuse of a minor are also reported to law enforcement, Linhart said.
Victims of alleged abuse have come forward across the country in recent years.
After allegations about Curl, 62, were revealed, his club, Curl-Burke, changed its name to the Nation's Capital Swim Club. The club, which has pools in the district and the Maryland and Virginia suburbs, has produced such swimmers as 15-year-old Katie Ledecky of Bethesda, who won a gold medal in the London Olympics this summer.
Last month, Mark Schubert, among the most decorated swimming coaches, was sued by a woman who said she was fired after trying to keep children away from another coach under investigation for sexual abuse. The woman, Dia Rianda, was a coach at Schubert's Golden West Swim Club in California. Schubert, who has coached such legendary swimmers as Janet Evans, had been fired as the national team's head coach in 2010.
After Riande filed her suit, USA Swimming issued a statement that "the resolution" of its relationship with Schubert "did not involve any cover-up of alleged sexual misconduct. … Rather, because of USA Swimming's commitment to safe sport, the agreement between USA Swimming and Mr. Schubert specifically required that if Schubert had, or in the future, received reliable information involving a sexual misconduct Code of Conduct violation by a coach or other member of USA Swimming, he would bring that information to USA Swimming in writing and would testify at a National Board of Review proceeding if requested to do so by USA Swimming."
Baltimore Sun librarian Paul McCardell and reporters Kevin Rector and Candy Thomson contributed to this article.