Plants and fish are going to depend on your maintenance of the water garden. If you were to build a water garden and never perform any type of maintenance, your fish, and plants will not be healthy and thrive, as you would expect. Of course, some plants are going to be very hardy and they will take over the pond. Those that are fast spreading will choke most other plants out. The fish are going to try to survive in the water that is murky and contaminated.
The water becomes polluted with disease and brings death of the fish and plants. A balanced environment in the water garden is what you have to achieve. Maintenance of the water garden is only a few hours a month, less than what you spend in weeding and maintaining many of your other gardens.
more of Pond Maintenance here