The Department of Conservation checking people getting on a ferry in Auckland on Saturday morning to make sure they are not carrying rats.
The screening is being done before 2000 athletes catch the ferry to Motutapu and Rangitoto islands, where mountain-biking and running events are taking place.
The islands are free of rats and mice and are close to being declared pest-free sanctuaries for endangered wildlife.
Three dogs and their handlers are carrying out the checks at the ferry terminal on Quay Street.
DoC says a rat was found in a van last week as it was about to be ferried to Motuihe Island.