The Australian Platypus Conservancy in conjunction with Upper Murrumbidgee Waterwatch started a regular platypus monitoring program in Queanbeyan in May 2009, recording platypus and native water rat sightings over the winter months when they're most active.

However new figures from the Conservancy have shown that sightings dropped from close to 40 sightings per 100 visits down to less than 20 in the winters of 2011 and 2012.

The wildlife group's February newsletter said that while many adult platypus survived the flood, juveniles in burrows would have been drowned.

"Sightings of both species remained unchanged in the first two months following this (2010) flood, suggesting that few (if any) resident adults drowned or were substantially displaced due to high flows. However, it's likely that many juvenile platypus and water-rats died when their natal burrows were inundated," the newsletter said.

"In the case of the Queanbeyan River, it is possible that the occurrence of a second sizable flood in early March 2012 may have contributed to persistently low numbers of platypus and water-rat sightings in the following winter."

However figures from the most recent winter period show platypus sightings back up to 0.28, or 28 sightings per 100 visits.

Local Landcare volunteer Tom Baker has been monitoring platypus for the Conservancy over the last eighteen months. He inspects as section of the river near Dane Street twice a week, and said he was pleased to see numbers increasing, including spotting five platypus on Australia Day this year.

However while Platypus are making a return, he said the sightings of native water rats was in decline both here in Queanbeyan, and across the country. Water rat sightings are currently at an average of seven sightings per 100 visits, a figure that's stayed static over the last three years.

"Water rats are quite widespread- including in coastal areas- but they're not abundant. Their numbers are falling.

"We've found that exact situation in Queanbeyan. We're seeing nothing like the numbers of native water rats that we saw before the two big floods. We do see on every now and then, but very occasionally," Mr Baker said.