Conservationists are calling for a crackdown on deadly yabby pots after up to half a platypus population in Victoria's east was wiped out by illegal nets.

Five platypuses were found dead inside two opera house traps in a dam connected to Labertouche Creek near Jindivick, east of Melbourne, last week.

The use of opera house nets are illegal in public waterways in Victoria, and people caught using them could face a $37,000 fine or up to two years in jail.

Researchers have been monitoring the Labertouche Creek platypus population since 2009, when numbers were decimated by droughts and the Black Saturday bushfires.

Department of Environment, Land, Water and Planning (DELWP) regional manager of environment and natural resources, Ryan Incoll, said the nets were death traps for platypuses, water rats, turtles and diving water birds.

"It appears the nets have been in the dam for some time, and individual platypuses have entered them over a long period," Mr Incoll said.

"One net contained three dead platypuses, the other contained two."

Five drowned platypuses retrieved from Labertouche Creek, east of Melbourne. ( Supplied: CESAR Australia )

Animals find their way into the nets, become trapped and ultimately drown.

Mr Incoll said the deaths were concerning but not uncommon.

"We remind the community that it is illegal to use or possess opera house nets in, on, or next to all Victorian public waters," Mr Incoll said.

"DELWP is continuing to work with fisheries officers throughout Victoria to detect and deter people from illegally using opera house nets.

"We want to deter lazy fishing practices and the selfish use of illegal nets."

Population was slowly recovering after fires, drought

CESAR Australia senior wildlife ecologist Josh Griffiths is part of a team that has been monitoring the Labertouche Creek platypuses for nearly 10 years.

He said the deaths were a blow to the population, which had been slowly recovering in recent years from fires and drought.

"We would estimate there is only 10 to 15 resident platypuses in Labertouche Creek … the fact five have been killed needlessly is a massive setback for the population," Mr Griffiths said.

"They're one of our most iconic species. I'm sure they're not worth a little feed of yabbies."

Mr Griffiths said while it was unlikely sale of the nets would be banned, people needed to be educated about the risks they posed to wildlife.

"We probably hear about [deaths] several times a year, usually during the summer months," he said.

"The reality is there are probably thousands of these nets out there, and we only hear of a fraction of these incidents.

"Potentially there are over 100 platypus that could get drowned in these just in Victoria alone. It's quite an issue."