In the one corner are Canberra's good administrators, armed with multimillion-dollar strategies to rid the Murray-Darling Basin and Canberra's lakes of the dreaded introduced pest.

In the other are the upstanding members of the Sydney Coarse Angling Club, which proudly proclaims its ''100 per cent catch and release of all fish (no exceptions)'' philosophy.

Sooner or later these opposing camps were going clash head-on, and they did last Friday, Saturday and Sunday.

Competing anglers pulled out 1000 carp from Lake Burley Griffin at the weekend. Then, staying true to their credo, they returned them all to the water.

A spokesman for the club, Howard Hill, said reducing carp numbers would do more harm than good because the lesser number of fish left in the lake would breed more, to outnumber those caught and killed.

He said 37 anglers had competed at the weekend and bigger national and Australia-versus-New Zealand events were planned for February. More than 3500 kilograms of carp were caught and released at the last national event in Canberra. The tournaments are at odds with a key strategy of the Upper Murrumbidgee demonstration reach clean-up program, from Bredbo in NSW to Casuarina Sands in the ACT.

The program aims to improve the river's health for native fish, and supporting it are ''carp out'' events, when thousands of anglers remove as many carp as they can from where they breed and congregate, especially in Lake Burley Griffin. Native fish, including Murray cod, that eat carp are released in the same water.

Conflict over carp in the ACT has been apparent since 2010, when the demonstration reach strategy was released, with the policy's authors noting that coarse fishing tournaments resulted in the capture and release of several tonnes of carp.

''Such exemptions clearly conflict with the intent of this carp-reduction plan,'' they said. ''In NSW there are similar issues, with it not being illegal to return carp to the waterway after capture.''

A Canberra ecologist and a longtime fishing commentator, Bryan Pratt, estimated that about eight million eggs were taken from a single carp captured in the ACT recently.

He said multiplying the tens of millions of carp in Lake Burley Griffin with the eggs they carried explained why rod-and-line fishing, netting, trapping and even lowering the lake's level during spawning would never eradicate the pest.

Dr Pratt said that other than genetic and viral methods of control, it was unlikely that Lake Burley Griffin would ever be free of carp. ''Possible, yes; probable, no,'' Dr Pratt said.