More than 12,000 people living near California's Lake Piru have signed a petition calling for better protection of swimmers following the disappearance of actress Naya Rivera on Wednesday.

The 33-year-old Glee star is thought to have drowned after hiring a boat with her four-year-old son before jumping into the water for a swim.

The search is ongoing for Rivera and should it be confirmed that she has died, she will become the ninth person to drown in the lake since 1994.

The lake is man-made, has strong currents and contains a lot of debris that can easily entangle and entrap swimmers.

The petition states: "Locals of Ventura County don't go to Lake Piru for this reason! Tourists have no idea what they're getting into. Lake Piru needs signs.

"We're tired of waiting. We need justice for all those who got lost at Lake Piru. Put up the signs."

TMZ reports that signage exists to warn people entering the lake from the shore but claims that people swimming via boats "don't seem to get the proper warnings".