Whitewater princess Jess Fox has made canoe slalom history but the sweetness of a rare K1 and C1 slalom double also held two bitter aftertastes in Slovenia.

Controversy reigned on the final day of World Cup 4 in Tacen overnight when Fox became the first woman to win gold in both K1 and C1 boats at the same Cup event.

It only occurred due to a bizarre re-run of the kayak final after the London Olympic silver-medallist bombed out as the last paddler down the course.

A power outage further up the river sparked a 15cm change in water levels, creating a disadvantage for Fox and other leading competitors, forcing organisers to call for a re-run.

It cost the 19-year-old's teammate Ros Lawrence a maiden World Cup medal in the K1 after she produced a sterling second in the initial final.

Lawrence was unsurprisingly upset by the ruling, eventually finishing ninth (10.29 seconds behind victor Fox) to rub salt into the wounds of a challenging season.

"It was a bizarre day," Fox said from Braitislova on Monday. "I really felt for the girls who finished first, second and third after that run.

"Ros was second and to be told to do another run ... I know how I'd be if I was in her position.

"I had a shocking run in that (first) final, with a really big mistake, and then got a second chance. I thought how lucky and made the most of the second chance."

The K1 triumph, beating Austrian star Corinna Kuhnle by 0.34s, was Fox's long-awaited first K1 gold and came after she continued her domination of the C1, winning her third canoe World Cup final this year.

The K1 and C1 double has been achieved by men before, most recently by British champion Dave Florence in Cardiff, but this was the first time for a woman.

It further stoked the desire of Fox and Australian Canoeing, lobbying for gender equity, to have the C1 event included in the Olympics.

As it stands the K1 is the only female whitewater medal at the Games, while men have three (K1, C1 and C2), giving the sport the second lowest female participation rate of 25 per cent (only higher than boxing).

"Afterwards I realised it was great for me to do that but I can't at the Olympics," she said. "It's sweet but it hits home because you realise there's not as many opportunities for women in our sport.

"We're behind other sports in the way we address gender issues and that should be a concern to the ICF (International Canoe Federation).

"At this stage it seems like they're still discriminating against women."