Inland Waterways OzFish president and co-founder Matt Hansen made the announcement on Wednesday, admitting the committee was "reeling" after making the difficult decision.

"It's very sad, it's our 10^th anniversary since starting the classic as well," Hansen said.

"But the fish come first. We've been all about the fish for a decade and we're certainly not about to put further pressure on a system that is clearly under pressure."

Fish at the lake have been showing signs of stress, Mr Hansen said, with recreational anglers reporting red, bloody spots on fish known as Lernaea.

A genus of copepod crustaceans commonly called anchor worms, Lernaea are a parasite that affect freshwater fish.

The female Lernaea burrows into the flesh of a fish and transforms into an unsegmented, worm-like form, usually with a portion hanging from the fish's body.

Following advice from NSW Department of Primary Industries Fisheries, as well as Water NSW - including the "very, very bleak" forecast of below average rainfall for at least six months - organisers made the call to cancel the 2019 event.

"It just wouldn't be the right thing for us to promote fishing while the fish are sick like this," Hansen said.

"Water quality is the issue. It's time that we give that fishery a rest until we get some rain."

Hansen thanked the "vast majority" of this year's sponsors for committing to 2020, as well as the community for "so much support over the last decade".

"This will not stop the work of the Inland Waterways," he said.

"We've been good little savers so we have more than enough funds to keep the River Repair Bus and our re-snagging projects going. It's onwards and upwards."