But the not-for-profit organisation promoting healthy rivers is fearful of retail chains and online outlets selling large numbers of the traps without warnings.

They are cheap, nasty, disposable and reap a grim catch of drowned platypus, turtles, water rats and diving birds like cormorants in the Murrumbidgee River, other streams and lakes around Canberra.

Bought over the counter and on-line for as little as $5, they are so cheap fishermen leave lots of them out in the water overnight, or lose count and leave them behind.

RiverSmart chief executive Bill Phillips said every retailer was willing to display the posters. Some even put them inside the traps.

''Our biggest concern is not the guys dedicated to fishing tackle,'' Dr Phillips said. ''The bigger concern is we are starting to detect the bigger chain stores are starting to dabble in this market.

''The online sellers are the worry. Unlike in the specialist stores, in these situations it seems no one is advising purchasers of the restrictions which apply, and that's a major concern,'' Dr Phillips said.

ACT Parks and Conservation manager Brett McNamara said Bear Grylls documentaries encouraged misguided people to try catching fish with homemade traps and set lines which killed wildlife.

''The set lines are insidious things. They have a rubber band and line and just sit there and anything that floats by grabs it. They are death traps, really.''

People from non-English speaking backgrounds, where fishing is unregulated in their home countries, posed another challenge.

''People are heading out with homemade devices, not realising or not appreciating the impact the lines and traps have on air-breathing monotremes like platypus. They don't have them back in the home country.''

Extensive new rock reefs in the enlarged Cotter Dam, where fishing was illegal, would likely increase populations of fish.

''That will be a magnet for people to go fishing. We are very conscious of that, in terms of patrols, education and awareness.''

Mr McNamara said rangers could rely on a good relationship with the fishing fraternity to remove any traps they found, photograph them and pass on information.

Legally no more than 10 baited lines are allowed for taking yabbies.

For fish, no more than two rods or hand-lines with no more than two hooks per rod or handline are allowed. Hoop nets must not be used in the Murrumbidgee River Corridor nature reserves. Since January last year, 12 infringement notices have been issued for illegal fishing gear.