Trapa natans form in large mats along the surface of water. These mats cause significant competition against native plants for space and for available nutrients. For animals that favor and ingest these plants, they are provided with a severe lack of nutritional value and may be detrimental to their health. Lower levels of dissolved oxygen in the water systems may occur in response to the water chestut decomposing after blooming. This encourages algae blooms and eutrophication of lakes. The spiny fruits produced by these plants can cause health risks to domesticated animals by possible foundering dogs and horses. The extensive spread of water chestnut can also reduce recreational value of streams and lakes by impeding fishing, hunting, swimming and boating.