Foothill’s Marcoux Right at Home in the Pool : Swimming: Senior felt burned out as a freshman. Now she leads Knights into tonight’s Southern Section Relays.

Sionainn Marcoux glided through the water Thursday, warming up for the preliminaries of the Southern Section swim relays. Her motions were effortless and graceful, just a natural-born swimmer loosening up for a race.

Marcoux, a senior at Foothill High School, was in her element. In water, she is considered one of the top female swimmers in Orange County.

On land, well . . .

“You ever hear the phrase, ‘A fish out of water?’ ” Foothill Coach Tom DeLong said. “She always seems to trip over something or run into things.”

But in the pool, Marcoux has been a standout swimmer since she was a sophomore at Foothill.

In fact, she’s probably the best on a team that figures to be one of the favorites in the Southern Section Relays at the Belmont Plaza Pool in Long Beach. The finals will be at 7 tonight.

“I think I’ve surprised some people with the way I’ve developed as a swimmer,” Marcoux said.

Even Marcoux has been surprised, considering that before her freshman year she was tired of swimming.

Marcoux has been swimming competitively since she was 5. She started with the Mission Viejo Nadadores, but changed club teams when she was 9 because the drive from Tustin was too long.

Marcoux then swam for the Southern California Aquatic club team, which is located in Tustin, for four years. But by the time she was a freshman, Marcoux said she was feeling burned out.

“I was really going through the motions,” Marcoux said. “I would skip workouts by telling the coach I had too much homework. Then I would go home and rot in front of the television. I thought I had leveled off as a swimmer.”

The Southern California Aquatics Club had been through three coaches during the time Marcoux swam for the team. But when Everett Uchiama became the coach in 1986, the situation stabilized.

“Workouts just seem to be more fun with Everett as coach,” Marcoux said. “I really can’t say why. But I just started getting interested in swimming again.”

Marcoux said swimming for the Foothill team has been a welcome break from the rigorous schedule she had with her club team.

“That happens a lot with swimmers,” DeLong said. “When you swim for a club team, it can be very serious. It’s not as much of a team event. In high school, there is more team spirit, with everyone encouraging each other.”

Marcoux made the Foothill varsity as a freshman and as a sophomore established herself as promising young swimmer.

She finished fourth at the Southern Section 4-A meet in the 200- and 500-yard freestyles, setting school records in both. Marcoux broke Andriane Schussler’s records with a time of 1 minute 51.69 seconds in the 200 and 4:56.03 in the 500.

As a junior, Marcoux slipped a little--if seventh-place finishes in both events can be considered slipping. She didn’t qualify for the championship race in either event, but won the consolation races.

“I was just worn out last year,” Marcoux said. “We had a lot of dual meets late in the season and it took a lot out of me. This year, the meets are spaced apart more. It’ll be easier at the finals.”

Marcoux is on a pace to break both records again, which is her individual goal for the season. Her other goal is to help the Knights win their first Southern Section title since 1974.

“The whole team is dedicated to winning the title,” Marcoux said. “That’s why you swim in high school. You do a lot of individual stuff with a club team, but you’re part of a team in high school. It’s a lot more fun.”

Of course, not all the fun was fun.

It was the camaraderie of high school swimming that led to her two injuries.

As a sophomore, she needed two layers of stitches after cutting her foot while taking part in a toilet-papering expedition. She cut her knee the following year under similar circumstances.

Marcoux said she has received a great deal of teasing from her teammates and coach about her mishaps.

“She’s a walking example of Murphy’s Law,” DeLong said. “Anything that can happen, will happen to Sionainn.”

DeLong may like to tease Marcoux, but he said that she is one of the best swimmers to come through Foothill.

Marcoux, who will attend Stanford next year and try to make the Cardinal swim team, also is becoming known on the national level. Two weeks ago, she placed at the U.S. junior nationals for the first time, finishing 14th in the 1,650-yard free.

“Sionainn has really come a long way,” DeLong said. “When she got to Foothill, she was a little tired of swimming. She had that, ‘What-am-I-in-this-for attitude.’ But that didn’t last. She’s become an outstanding swimmer.”

Even if she can’t swim freestyle and chew gum at the same time.