Artificial reefs made up of "fish hotels" have been built by volunteers in South Australia's Riverland to mimic the natural logs and snags that are essential habitats for native fish species.

More than 15 tonnes of red gum logs, hammered into cube-shaped structures, have been dropped to the bottom of Lake Bonney, a freshwater lake attached to the River Murray.

Coordinator Kym Manning said he started the project four years ago to help native fish populations.

"Our hotels in particular are about 1.5m square and about 1m high. We put a buoy into the water and drop between four and six hotels around each buoy. That designates one reef," he said.

The 4km trail now consists of 20 reefs, and Mr Manning said it was a hit with the fish.

"I've been over in my boat several times with a sounder. It definitely says there's fish on them. Not all the time … they move on this habitat trail," he said.



Coordinator Kym Manning with the last fish hotel at Lake Bonney. ( ABC News: Brittany Evins )

Catching up with other states

Mr Manning said it was a case of SA playing catch-up to other basin states in creating native fish dwellings.

"We are so far behind it is not funny," he said.

"They started doing these things in Victoria and New South Wales at least 10 years ago."

Peter Teakle, director for RecFish SA, the peak body for recreational fishing, agreed.

He said it was pleasing to see some action being taken locally.

"Habitat rehabilitation has been going on for many years interstate and it's been a positive venture by all parties concerned, whether it be government or local groups," he said.

Riverland volunteers gather around the last fish hotel constructed for the 4km fish trail. ( ABC News: Brittany Evins )

Passion poured into project

In what he initially forecast as a two-year project, Mr Manning has now clocked up more than four years working on his fish hotels.

He said despite it being a time-consuming project, he hoped the work to boost fish numbers would continue.

"I would love to put tonnes and tonnes more in. It really needs it," he said.

"It is fantastic for the area to have a lot of native fish, and it is amazing the distance people will travel to try and catch a fish.

"All volunteers, nobody gets paid a cracker here, not a brass razoo."

This structure is the last of the manmade native fish habitats to sink to the bottom of Lake Bonney. ( ABC News: Brittany Evins )

Gary Holder has attended almost all of the working bees, and said it was the local spirit and passion that made the project so special.

"Before I was in the wheelchair I used to go out on the boat with my son and throw the reefs," he said.

"You get little groups of guys that work well together on the drill and then building the reef."