The Rotorua harbour master is sick of swimmers putting their lives in harm's way.

A number of swimmers have been caught in ski lanes lately, despite clear signage warning of the danger.

Bay of Plenty Regional Council maritime officer Ross Powell says boats travel at up to 60 kilometres an hour in the lanes.

"You don't go and play on the motorway, you go and play in the fields or the park."

Ross Powell says the lanes are clearly marked and signposted.

"It's a ski lane, it's not a swimming beach. Boats often will be going too fast to be able to do anything, and the results will be extremely nasty."

Ross Powell says they'll be enforcing the ski lanes rigorously over the next few weeks, to ensure swimmers aren't hurt - or worse.