Rail cars leaked bunker fuel oil metres from summer homes bordering Lake Wabamun. (John Ulan/Canadian Press)

As ice melts on Alberta's Lake Wabamun, oil and black tar are rising to the surface, the poisonous evidence of a toxic spill last summer.

A CN train derailed in August, dumping 730,000 litres of fuel oil and wood preservative into the lake, about 50 kilometres west of Edmonton.

Health authorities have warned people to steer clear of tar balls surfacing on the lake during the spring thaw.

The tar is made up of chemicals from the derailment, said Dr. Gerry Predy, Capital Health's vice-president for public health and medical officer of health.

"The best thing is to leave the tar balls alone, making sure children and pets do not pick them up or swallow them," he warned in a news release.

A health advisory has also been issued warning people against using lake water for drinking or washing clothes.

Rudy Bird of the Paul Band, who is supervising the cleanup of 12 kilometres along the eastern shore of the lake, said he expects the cleanup to take years to complete.

Bird says those who live on the reserve are no longer hunting game because the animals often drink from the lake.

Alberta Environment has yet to complete its investigation of the spill.