Is your water garden having a RIPPLE effect on Michigan's waterways?

While water gardens add beauty to backyards, it is important to be aware of the risks associated with aquatic invasive species and to prevent escape.

orange fish in a pond with floating plants
Koi and water hyacinth are popular additions to backyard water gardens. They sometimes escape into natural waterways during flooding events. To prevent this, build water gardens away from other waterbodies.

Wildlife sightings, soothing sounds and scenic beauty are a few benefits of backyard water gardens. While exotic fish such as koi can be attractive and friendly additions, and non-native ornamental plants such as water hyacinth add vibrant color to your yard all summer long, neither are native to Michigan. If they are let loose into our lakes and streams, they can have long-lasting, detrimental impacts. Many water garden fish and plants from outside the region are hardy and grow rapidly making them easy to care for, but these characteristics can also cause them to be invasive if they escape from water gardens and reproduce in lakes and rivers.

Invasive water garden plants and fish can enter Michigan’s lakes and streams in a variety of ways. Frequently, water gardeners release pets such as koi and goldfish when they are no longer wanted. This often happens in the fall when homeowners are preparing their water gardens for winter and notice an abundance of fish. Many water gardeners are surprised to find that their goldfish have flourished, especially in water gardens with floating plants and rocks that protect them from predators. Flooding is another way that non-native fish and plants can escape water gardens. Thus, the best location for a water garden is away from other waterways.

While releasing unwanted fish into lakes and rivers may seem humane, the consequences to the environment can be devastating. Koi for example have been found to cause outbreaks of Koi Herpes Virus, a highly contagious disease that exclusively impacts common carp. It spreads to wild populations when koi from backyard ponds are released into the wild. In addition to disease, water garden fish can also outcompete native species for food and habitat causing long-term impacts.   

If you have an unwanted fish or plant in a water garden, never release it. Environmentally friendly alternatives include giving or trading it with another water gardener or connecting with a local pet or garden store. Some local retailers will take unwanted fish and plants to stock their ornamental display ponds. Retailers also have connections with rescue groups that can assist with rehoming.

Aquatic species of concern

Two common water garden plants of particular concern are water hyacinth and water lettuce. Water hyacinth is a very showy plant and features light purple flowers and dark green, glossy round leaves. As its name implies, water lettuce looks like an open head of lettuce and has thick, hairy leaves. Both float on the surface of water and are easy to care for because they reproduce throughout the summer. While they are commonly available for purchase, water gardeners should use caution. Water hyacinth and water lettuce are both highly invasive and are on the Michigan aquatic invasive species watch list. In the southern United States water hyacinth and water lettuce clog waterways and obstruct boat traffic and impact wildlife. They can also prevent sunlight from penetrating the water, thereby reducing beneficial native aquatic plants, which many aquatic organisms rely on for shelter and food. Water hyacinth and water lettuce have both been found in Michigan in natural waterways. Water lettuce was discovered in 2020 in the Clinton River spillway and water hyacinth has been observed in the Detroit River and in western Lake Erie for multiple years. When found in the wild Cooperative Invasive Species Management Area staff will remove the plants by hand and monitor the location. If you spot water hyacinth, water lettuce or any other organism commonly found in water gardens in the wild report it to the Midwest Invasive Species Information Network.

When choosing plants consider asking your local retailer for native species. There are many native plants including white water lily, pickerelweed, and marsh marigold, that can add beauty to water gardens without as many risks. The State of Michigan has laws restricting and prohibiting the sale of some organisms, including plants and fish in the water garden industry. However, it does not include all potentially harmful species.

Tips to reduce the risk of invasion

If you have a plant or fish in your water garden and would like to get rid of it, never release it into waterways. Follow the RIPPLE: Reduce Invasive Pet and PLant Escapes program guidelines to protect your water garden and the environment.

  • Plants should not be composted; bag it and put it in the trash.
  • Inspect and rinse any new plants to rid them of seeds, plant fragments, snails and fish. Often aquatic plants have unwanted hitchhiking organisms attached and some can be invasive.
  • Build water gardens well away from other water bodies to prevent them from overflowing to nearby lakes and rivers during heavy rain events.
  • Give or trade unwanted fish or plants with another water gardener or reach out to a local retailer who may have connections to rescue groups.
  • Contact a veterinarian or pet retailer for guidance on the humane disposal of animals.

The Reduce Invasive Pet and Plant Escapes (RIPPLE) program is a partnership between Michigan State University Extension and the Michigan Departments of Natural Resources, Agriculture and Rural Development, and Environment, Great Lakes and Energy and receives funding from the Michigan Invasive Species Grant Program. RIPPLE educates pet and garden retailers and hobbyists about proper disposal of organisms in aquariums and water gardens to prevent the introduction and spread of invasive species.

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