PESTICIDE was not the cause of beach worms deaths near Seal Rocks, a NSW Environment Protection Authority investigation has concluded.
Commercial fishermen reported the dead worms on Yagon beach on June 3, sparking laboratory testing to find the reason behind their demise.
Department of Primary Industries scientists tested pipis, sea water and sand in addition to the worms but found no evidence of algal toxins or pesticide chemicals.
They also ruled out disease.
National Parks and Wildlife had sprayed bitou bush in the area during May and June but the EPA said a review led them to conclude the worms died due to natural causes.
Executive director regulatory operations Carmen Dwyer said the EPA found losing two metres in sand depth and 20 metres of the beach after large storms had reduced the habitat available to the creatures.
"Groundwater levels were closer to the beach after significant rain in March 2021 and then prior to the beach worm mortality event," Ms Dwyer said.
"The EPA found evidence that low tides and calm seas at the time of the deaths did not allow the marine water to mix with the fresh groundwater egress on the beach face. Beach worms cannot handle these drastic changes in salinity and subsequently died."
A precautionary closure of commercial shellfish harvesting from the beach was lifted on June 18.
