Some surprising items have been uncovered as the water level was lowered in Lake Tuggeranong to allow a regular, five-year inspection of its infrastructure.
Teams including divers have been inspecting five dams, ponds and lakes across Canberra as part of the ACT government's ongoing dam safety program.
The inspection of Lake Tuggeranong has been completed, with Tuesday's rain helping to start to top up the lake once again.
From July 27, dam water levels were lowered by about half a metre to allow safe access to inspection areas of Gungahlin Lake, Lake Ginninderra, Lake Tuggeranong, Whitlam Dam and Yerrabi Pond.
Roads ACT is in charge of the dam lowering program.
Its executive branch manager Tim Rampton said the stilling basin beneath the spillway of Lake Tuggeranong was also pumped as part of the program, revealing some interesting finds.
"When we removed the water from the stilling basin, we also found 20 shopping trolleys, two electric scooters and three bikes," Mr Rampton said.
"We did manage to find some quite large Murray cod. We found five Murry cod and four Golden perch which had obviously made their way over the spillway and into the stilling basin. So we relocated them back into the main dam.
"We also found some Murray cod and perch in the Gungahlin stilling basin as well."
Mr Rampton said lowering the water was a bit like pulling the plug in a bath, by opening a valve on the dam wall.
"We have a valve that we can manually open. We don't need to go under water to open it. There's a valve we can open on the other side [of the water]," he said.
"So we can release the water at a measured rate. It's important we don't release it too quickly as we don't want to cause erosion and other impacts downstream.
"At the moment with Tuggeranong all our main inspections are now complete and we don't need to release any more water. So that's now into its filling stage. Some of the other dams, we made need to release a little more water after [Tuesday's] rain."
The inspections assess key infrastructure including embankments, spillways, outlet valves and other critical assets for signs of deterioration or potential failure risks.
Mr Rampton said nothing of concern was found at Lake Tuggeranong.
"Only minor things we need to address," he said.
"We're still waiting for our engineer's report to come through, but they haven't highlighted anything substantial we need to look at. It's all gone well."
There were also some unusual finds in one of the dams further north.
"When we lowered Whitlam Dam, we actually uncovered eight illegal yabbie traps," Mr Rampton said.
"We disposed of them because we don't want native fauna getting stuck in there, things like turtles and so on. It was nice we would able to uncover those traps."
Mr Rampton said the dam lowering was necessary every five years.
"By simply lowering the water level, it allows us to inspect some assets that lie just below the water surface normally, but it also allows us to get our teams and engineers in there so they can do their inspections safely," he said.
"So we're looking for any signs of deterioration or maintenance we may need to do and any potential risk to that asset.
"Over the last week, we completed our diving inspection. So, we actually had divers in the water looking at the face of the dam and the outlet infrastructure, just to make sure everything was all good under the water.
"Again, that's not something we do all the time, but it's nice to have those actual visual inspections under the water."
