Northern Territory park rangers are asking tourists and residents not to wear insect repellent or sunscreen while cooling-off in park waterways because the chemicals kill aquatic animals.

Kakadu National Park senior ranger Greg Miles says swimmers should wear long-sleeved clothing if they want to prevent sunburn and insect bites.

He says water quality in the bush is particularly important.

"Because you've got so many animals that live in there, fish and turtles and file snakes and what not, that are entirely dependent on water quality for their survival - particularly as the dry season gets older and the water levels shrink - that means that it condenses any pollutants that might be in the water," Mr Miles said.