Some people have the misconception that water gardens will attract and produce mosquitoes. This is not the case. There are certain things that can be done to eliminate mosquitoes all together from water gardens.
When designing your water garden provide lots of plants for the decorations. These plants will attract certain insects that will feed on the mosquito larva in your water garden.
Also water gardens are also known to attract dragonflies and damselflies. These insects are great to keep your mosquito population to a minimum. They will eat hundreds of mosquitoes a day. Also you may want to add a few fish to your water garden. The fish will consume the mosquito larva that grows in the water also. A water garden actually will help fight against mosquitoes. Dragonflies and damselflies are often referred to as Mosquito Hawks because they eat so many and will also feed on the larva. Also try to keep your water gardens as deep as possible. Mosquitoes are subject to pick out shallow bodies of water to lay their eggs which is also called larva. Also make a drainage pipe for your water gardens. Sometimes it is a good idea to change your water and keep your water garden as clean as possible to keep mosquitoes away. Also if you have a waterfall in your water garden your water will always be moving and this will also make it difficult for mosquitoes to lay eggs in your water garden. You can find more information on this from your local home and garden center and also from an online plant nursery.
Source of Information on Keeping Mosquitoes out of Water Gardens