DE SOTO, Mo. -- Missouri regulators are investigating at Spring Lake, where residents and swimmers have received serious, even fatal, electrical shocks.

The Missouri Public Service Commission is looking into the cause of electric voltage that shocked a resident over Memorial Day weekend. The lake has been closed.

Three years ago, four teens were immobilized by an electric current in the lake. One drowned, two had to be resuscitated and the other was pulled to safety.

The St. Louis Post-Dispatch reported Friday that commission representatives went to the lake Wednesday to try to figure out why people are being shocked there.

"Consumer safety is the most important to us and we're trying to make sure the lake is safe," said Wess Henderson, the commission's executive director. "We want to get it fixed before there are any more fatalities."

AmerenUE was ordered to pay $2.3 million to the families of the 2006 victims, but the electric utility denied its system was to blame.

Members of the Public Service Commission ordered staff to look into Ameren's work after learning that Shawna Theel, 25, was shocked while dangling her toes in the lake from her father's dock, which is across from where the teens jumped in three years ago, Henderson said.

"There seems to be a recurring problem here," Henderson said.

"Our staff is down there now to determine the cause of the problem, and once they determine that, based on what they find, that will dictate what we do going forward."

Ameren employees are cooperating with commission staff, Fox said. "We won't be done until we're satisfied and the dock owners are satisfied that everything has been addressed," he said.

At trial earlier this year, Ameren's attorneys blamed faulty wiring on the dock from which the teens jumped as the cause of the voltage. Fox said Ameren would work with the homeowner's association to teach residents about proper dock wiring.

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Information from: St. Louis Post-Dispatch, http://www.stltoday.com