Hello,

Thank you for reaching out to Extension. So we can better assist you with this issue, can you please provide a little more information about your pond:

Approximately how big and deep is your pond and what do you use it for? Is the pond connected to a stream, and/or do you have a water circulation device installed? Where in the state is your pond located?

Lastly, it would be wonderful if you could provide some clear photos of the pond, as well as the grass and algae of concern. 

Thank you for the additional information. The abundance of aquatic plant growth suggests that the pond has high levels of Phosphorous and Nitrogen coming from the runoff. This is important to consider because any effort to control the vegetation could fall short and plants will likely grow back quickly if these nutrients are not reduced. Additionally, those grasses are serving to soak up some of the nutrients, so the best course of action would be to minimize the nutrients that are entering the pond before considering options to control the vegetation.The key management practice will be to prevent runoff from lands that may contain high sources of nutrients such as fertilizer, a leaking septic tank, and waste from pets, waterfowl, or livestock. Any erosion coming off the banks of the pond will also contribute excess sedimentation and further nutrient storage. Planting native trees, shrubs, grasses, and forbs around the border of the pond will stabilize the banks and increase water infiltration of the soil, preventing sediments from entering the pond.

To manage the existing vegetation and nutrients in the pond, dredging the sediments and controlling vegetation can help. If sediments are dredged, check with the Department of Environmental Quality regarding proper disposal of dredged material. I suggest skimming away the floating vegetation, as aeration will help minimize plant growth and matting. When applied at the correct time, aquatic herbicides and algaecides can be a cost-effective and successful way to manage the grass and algae. The resource below gives additional recommendations for manual vegetation control, as well as herbicide and algaecide application.

Grass carp are a non-native fish species that can be used to control unwanted aquatic plants. In Oregon, grass carp are a controlled species and require a grass carp stocking permit. Only sterile grass carp from an approved supplier are allowed, and the permit application must be approved by both Oregon Department of Fish and Wildlife district and regional biologists. Grass carp will rapidly consume large amounts of your pond vegetation and can even damage the riparian area around the edge of the pond. In the absence of aquatic vegetation, they will dig into banks to uproot and eat riparian plants. 

Other resources:

Woodland Ponds Field Guide

ODFW Fish Stocking FAQ