The annual On the Fly festival, which uses the Mataura River in Gore as a backdrop, held activities for the whole family on Sunday.
There were go-karts, face painting, live music, food trucks, a beer garden and information stalls.
Environment Southland (ES) had an interactive display with buckets of water holding samples of river matter, including the aqua invertebrates the brown trout from the river like to eat.
When asked about the safety of swimming in the Gore end of the river, Mr Sullivan said it was safe for humans, as long as you did not open your mouth to ingest the toxic algae.
The algae occurs naturally in the river but multiplies as the water gets warmer.
Mr Sullivan said dogs should not swim in the river as they were attracted to the smell of the algae and would try to eat it.
There was also a demonstration using magnetic fishing rods focused on its "check, clean, dry" programme and designed to teach Southland river and lake-goers to not spread freshwater pests.
Also at the Fish & Game tent was a tank filled with baby rainbow trout, and there was a competition to guess how many were in the tank.
Fish & Game officer Steve Dixon had picked up the juvenile fish that morning from Macraes Flat Trout hatchery.
He had a trailer filled with even more fish that Otago Fish & Game were taking to populate Lake Thomas, a shallow lake to the east of Lake Te Anau.
"There’s still a lot of Kiwis that catch for the dinner table," Mr Dixon said.
Otago Fish & Game’s Bruce Quirey agreed, saying it was a great family activity.
"[It’s a chance] to connect and take time away from busy lives," he said.
An interactive mural of the river festival, designed by local teacher Meg Cloete and face painter "The Big Yellow Paint Box", was on board, illustrating rainbow trout, marine life and mermaid designs on children’s faces.
