A local wildlife spotter found the drowned animal caught inside a yabby trap about 50 metres downstream from The Basin at Kentlyn on Monday.

Local koala expert, environmentalist and Advertiser columnist Robert Close was upset the animal was dead, but said the discovery of the fully grown, 48cm-long male platypus was still more proof of their presence in the river.

"It's quite amazing we should have two sightings in two weeks when I've been looking for 20 years," Dr Close said.

"The chance of having two incidents within two weeks is very slim."

A dead platypus discovered in the Georges River near Old Kent Road at Kentlyn a fortnight ago was the first confirmed sighting in the area in years.

At the time, Dr Close said the unusual creatures were rarely found in the area and several past sightings were unconfirmed.

Dr Close said the fact both platypuses were found within 3.5 kilometres of each other, close to the junction of the Georges River and Punchbowl Creek, could be significant.

"My thought now is that they're coming out of Punchbowl Creek, which comes out of army land, so it is quite protected and runs right into The Basin."

"I think it will certainly be worthwhile to investigate that creek. We've never looked at it before.

"In just two weeks to have two animals killed because of the acts of thoughtless fishermen is devastating, but it does give us the impetus to keep looking."

National Parks Association Macarthur branch member Julie Sheppard said the discovery of another dead platypus in the river was extremely disappointing.

"But again it shows they're there, they are in the Georges River."

Ms Sheppard said the discovery reinforced the dangers traps posed for native wildlife.