By reducing the use of fertilizers or by reducing the runoff from farmland after rainfall.
Explanation:
Farmers use excessive fertilizers on farms. This fertilizer is carried by runoff water to the nearby water body. Due to the addition of fertilizers, the water in the water bodies get nutrient enriched thereby causing excessive growth of algae in it (Known as algal boom). If farmers reduce the usage of fertilizers, or somehow take measures to reduce/stop the run off of water from farmland, then this problem of algal boom can be reduce.
If there was a larger population of rabbits than dandelions, and the rabbits only ate the dandelions, they would eventually run out. then the rabbits would start to die too, since their main food source is gone.
