Best way to 'sterilize' stagnant water?

There are a number of small pools of stagnant water near my home which make marvellous breeding grounds for mosquitoes. What’s the cheapest and least toxic way to make these pools useless for hosting life?
Add salt? a bit of bleach?

Mosquito dunks. Small donut shaped floats that make tne water unable to host the larve. Cheep and avalable at your local TSC store.

Try a little vegetable oil. It will spread out in a thin film and this might disrupt the breeding cycle. Benjamin Franklin used to trick his friends on a windy day by waving his walking stick in front of a pond. He had oil hidden in the end of the stick and it would pour out when he waved it across the water. The oil spread a thin film which altered the film tension on the water and it smoothed out the pond.

are you trying to kill all life in the ponds or just the mosquitos?
Obviously the former is a big and dangerous job. (nuke em from orbit-its the only way to be sure)
for mosquitos-see the other posts though the mosquito pills are more effective than oil.

Sorry, they’re not proper pools of some size, they’re just little puddles that collect from the rain and then stand for weeks. Also I’m not 'Merkin, so that’s why I’m looking for simple non-specialist products available anywhere.