LONDON -- Carlos and Peggy Steffens' pool didn't resemble most of the aquamarine tanks that dotted Danville.

Theirs had 50 yellow water polo balls bobbing about at any given time.

Some got so water logged that they turned green.

Those balls, though, have helped the fortunes of the U.S. women's Olympic water polo team, which plays rival Australia on Tuesday in the semifinals of the London Games.

The United States (4-0) heads into the match with the help of starters Maggie and Jessica Steffens. The sisters will be counted on against a team the Americans have met in every women's Olympic water polo tournament, starting with the gold-medal match in 2000. The Aussies won that one. But the United States defeated Australia for the bronze medal in 2004 and won again in the semifinals in Beijing.

The Steffenses are among seven players with Bay Area ties that comprise a team trying to win its first Olympic gold medal.

Maggie, 19, delayed her entrance into Stanford by a year to train for the Summer Olympics. Though she is the team's youngest player, Maggie has quickly become the U.S. star with 12 goals in four games.

As the youngest of four, she followed her sisters and brother into the pool despite the family motto: "No mercy."

"Half the time we didn't let her play because she was too small," Jessica said at the Aquatics Centre here. "But that didn't stop her."

To play water polo in the Steffens household is something of a birthright.

Brother Charlie was a Cal star and older sister Teresa also played at Cal for a while. Then there are the cousins. Tons and tons of cousins who played throughout the East Bay.

"The best thing about my family, they made me who I am," Maggie said. "I've learned to never back down."

It's a trait that courses through the veins of this East Bay legacy clan.

To understand the complicated familial lineage, one must begin with the Schnuggs of Orinda. With 13 children, the parents sent their kids to the local pool in the 1960s to keep them occupied.

"I don't think we got out of bathing suits all summer long," Peggy Steffens said.

Peggy Schnugg met her husband, Carlos Steffens of Puerto Rico, through Cal water polo in the '70s. At the time, Carlos was a teammate of Peter Schnugg, a two-time All-American.

Another Schnugg, Sarah, married yet another Cal teammate, Mike Loughlin.

All told, 15 of the Steffenses' aunts or uncles attended Cal between 1967 and 1986. In two generations, 27 members of the extended family have attended Cal -- and many of those played Division I sports.

However, no one begrudges Maggie and Jessica Steffens for choosing rival Stanford.

Jessica Steffens, 25, is considered the trailblazer for the women's water polo subset along with cousin Stephanie Schnugg, a Cal standout from 2006-10.

When Schnugg and Jessica Steffens played for Monte Vista High, they pushed each other as the school's stars.

"They used to come out banged up and smiling," said Peter Schnugg, whose chance to play in the Olympics ended with the 1980 U.S.-led boycott.

Despite the Schnugg heritage, the kids never felt pressured to follow in the family business. Jessica Steffens said the cousins didn't know how good their parents and uncles were until meeting others who talked about it.

But "all the Schnugg kids knew you were supposed to play sports, you were supposed to be competitive and you were supposed to want to win," Jessica said. "That's where it all started."

All the kids reaped the benefit of playing under Maureen O'Toole, perhaps the most influential player in women's history. O'Toole coaches the Diablo Water Polo girls program where the Steffens -- and some of the Schnuggs -- developed.

O'Toole, the Cal coach in the 1990s, saw something special in Maggie Steffens and put her on teams with older kids twice her size.

That's when Peggy Steffens decided, "OK, I guess I'd better get used to this."

Thankfully she has adopted such an attitude. Jessica, a 6-foot defender who graduated from Stanford in 2010, wore a bandage over her right eyebrow after a game Friday against China.

Now Peggy Steffens is along for the ride, one the extended family hopes ends with the elusive gold medal.