Tempestuous weather is forecast for the weekend but that won't dampened the last leg of the Swim the Lake series in Rotorua.

The Rotary Rotorua open water swim at Lake Okataina is the fourth and final round of this year's record-breaking championships on Sunday.

This is the fifth year the annual swim has been hosted by the Rotary Club in conjunction with Swim Rotorua.

"Lake Okataina is such a beautiful place and people love the scenery, it's certainly a special race," race director Katrina Allison said.

"I'm praying that the weather isn't too bad but the open water swimmers are a hardy lot."

Sunday's swim offers the premier race of 6km and a variety of other distances - 3km, 1500m, 800m and 400m swims.

Around 100 competitors have entered across all distances with 50 per cent of the field from Rotorua and three international entrants from England and Australia.

Swim Rotorua will have more than 20 athletes competing with Bethlehem College student Emily Spear one to watch in the women's premier 6km race.

But last year's winner William Spear and up and coming star David Bowles will not compete.

Swim Rotorua assistant coach Bronwen Radford said it would be an "exciting open field" and was "delighted" by the growing success of the Swim the Lake series.

"It's wide open for the taking. We have some very exciting juniors moving through the ranks but in the premier 6km I expect a seasoned adult to take it," Radford said.

"The lake is a little way out of the area, it's a very unique race. It's iconic to the area and a beautiful spot.

"This series just keeps getting bigger and bigger especially with the number of youngsters. That's great because it promotes water safety and gives swimming confidence to the young."

The third event of the series - Legend of the Lake swim at Tikitapu (Blue Lake), was won by national 10km open water swim champion Matt Scott and Dunedin's Stefannie Gillespie took out the women's field, while the second Lake Rotoma Kiwanis Swim saw local Glyn Eason win over the 6km distance with Swim Rotorua's Spear the top female finish.

In the first event of the series John Paul College students Milla Theobold, 13, and Boles, 16, were the first female and male to finish the Hinemoa-Tutanekai 2km non-wetsuit race.

2017 Rotary Rotorua open water swim

When: Sunday March 12, 6km and 3km start 10am. 
Where: Lake Okataina
Field: 100 / 50 per cent Rotorua field / 3 internationals.