Six different course lengths will be on offer, with senior long and short course triathlons, junior long and short course triathlons and both a senior and junior duathlon.

Tri Horsham's Simon Mentz said organisers were hopeful of a big turnout of competitors and supporters.

"This year we would love to see in the region of 250-300 participants," he said.

"It is a great course for spectators too, so we are hoping for a big turn-out of people down at Sawyer Park.

"It's really a great spot competitors are constantly in sight of each other and spectators can always keep an eye on what's happening."

The junior events get underway at 4pm and senior events at 5pm, with the option of entering individually or in teams.

Mr Mentz said the different course lengths meant everyone could be involved, including families.

"There is something for everyone, people can enter on the day and even enter as a team," he said.

"The junior triathlon is open to all kids up to the age of 16 and parents can swim in the river with their kids to encourage them and help them along."

The long course triathlon incorporates a 500-metre swim in the Wimmera River, followed by a 20-kilometre ride and a five-kilometre run.

Race director Mark Pumpa hopes there will be support for competing triathletes as they ride up and down Barnes Boulevard.

"Hopefully we will get a few residents setting up in their front yard to cheer the competitors on and add to the spectacle," he said.

"Vehicles will still be able to use the road but we will have marshals and signs along the road to ensure the safety of everyone involved."

Mr Pumpa said athletes would travel from across the state, with entries from Melbourne, Geelong, Echuca, Shepparton and Albury.

Mr Pumpa said last year's Horsham Triathlon long course winner, Echuca's Steve Gray who is currently sitting second in the tri-series male 40-49 points tally would be returning to compete in the event he has won five times.

Online registrations close today at 6pm, but registrations are open on the day at the Horsham Angling Club clubrooms.

Horsham's event is the fourth triathlon in the maiden five-race Telstra Store Rural Tri Series.

Triathletes competing in the long course triathlon earn points towards the overall series, with prizes for a number of different competition age categories.

Mr Pumpa said people could visit www.trihorsham.com.au for more information.