This is good news for the fish and for plans to build a 75-gigalitre dam downstream on the Cotter.

As reported by The Canberra Times on May 20, the future of the $300 million project depended on the presence of a safe haven for the two-spined blackfish and the Macquarie perch.

In the ACT, the latter is essentially present only in the lower Cotter River, though it is occasionally found in the Murrumbidgee River.

In 2001 a rock-ramp fishway was built at Vanity's Crossing to enable the fish to move upstream past the road crossing on the Cotter River.

Initial results were disappointing, when it seemed the fish were not using the fishway.

But recent surveys indicate the Macquarie perch have moved upstream of the fishway and are breeding in a stretch of river that they have not occupied for at least 20 years.

Newly hatched Macquarie perch have been recorded in 23 of 25 pools surveyed, including 13 of 14 pools upstream of the fishway.

An aquatic ecologist with the Department of Territory and Municipal Services, Ben Broadhurst, said these findings were of national significance and marked important progress in understanding how to manage and sustain an endangered fish species safely.

He said it also seemed likely the two-spined blackfish were using the crossing.

This was important because the proposed Cotter Dam would flood the lower sections of the river where the fish had been living.

Chief Minister Jon Stanhope said research into the Macquarie perch had been funded by the ACT and Federal governments' national action plan for salinity and water quality, and the Federal Government's Natural Heritage Trust.