Female mosquitoes only require a few ounces of stagnant water to lay eggs in. This customer's old over turned slide was collecting rain and leaves.
This video is just one small portion of the water collecting in the slide. Hundreds if not thousands of mosquito larvae in development. Within a week they will be adult mosquitoes.
You can help prevent mosquitoes by removing anything that can collect water. Common culprits are buckets, tires, wagons and birdbaths. This video is of a 5 gallon bucket left in the neighbor's yard of a customer. Again, you can see the larvae in development.