One of Australia's most invasive water weeds has been discovered in a creek in the southern Perth suburb of Lynwood.

Water hyacinth has been found at Bannister Creek by a local natural resource management group.

It is thought the weed was dumped in a storm water drain or directly into the creek.

The Department of Agriculture says water hyacinth chokes up rivers, lakes and other waterways.

Department researcher Sandy Lloyd describes the plant as one of the world's worst weeds.

"It is a declared plant in Western Australia, prohibited from sale and it must be destroyed when found," she said.

It says suspect aquatic weeds should be reported to the department's Pest and Disease Information Service on 1800 084 881.