Naya Rivera's Presumed Drowning Angers Locals Demanding More Safety for Swimmers

Naya Rivera's presumed death has angered locals who know the hidden perils of Lake Piru, and now they're demanding more protection for swimmers whose lives are at risk.

More than TWELVE THOUSAND PEOPLE and counting have signed a petition ... demanding more effective warnings for swimmers who are clueless that the waters below are perilous.

The locals have reason for concern ... Naya would mark the 9th drowning death at Lake Piru since 1994.

As we reported ... when Naya jumped in the water, the visibility was 5 to 9 inches. Piru is not a natural lake, and its bottom is covered by trees and other debris, in which a swimmer can easily get entangled. The lake also has strong currents, making swimming difficult.

The petition reads, " ... people have been asking for years for the city to put up warning signs for swimmers. 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."

There are some marked swimming areas for those who jump in from the shore, but people on boats don't seem to get the proper warnings. It's perilous because just about anyone on a boat in the middle of a hot summer day is going to want to jump in the water to cool off.

Law enforcement sources tell us ... they don't know where Naya and her 4-year-old son, Josey Hollis Dorsey, were when they both jumped in the water. Josey got back in the boat and fell asleep. When authorities arrived, he told them Naya never returned.

Lake Piru does not have many lifeguards, and swimmers "are engaging in a hazardous recreational activity and do so at their own risk" ... according to its policy. Locals want to make it less risky ... thus the petition.