Wolffia, more commonly known as watermeal, is the smallest known seed-producing plant. A member of the duckweed (Lemnaceae) family, the very tiny, light green, free-floating leaves grow in dense colonies on ponds that have very little water flow.
Although many water birds enjoy snacking on watermeal, once introduced, watermeal can quickly cover an entire pond, blocking the sunlight and reducing oxygen levels in the pond.
For aeration system design and installation, as well as supplies and additional information, visit Splash Supply Co. in York, PA or call 717-751-2108.
Preventing Duckweed and Watermeal
Take a proactive approach to pond management. Use aerobic beneficial bacteria and sludge-digesting anaerobic bacteria to reduce muck and the nutrients watermeal needs to grow. 
Using Aeration to Control Watermeal & Duckweed
Killing off watermeal with a chemical control can lead to fish loss due to rapid loss of oxygen in the pond when the plants die and decay, so we recommend mechanical removal as your first option. Â A properly designed aeration system uses air bubbles to create circulation that pushes the watermeal to the edge of the pond, where you can easily remove it with a pond net.
Chemical Control
Broad spectrum contact herbicides are available and can quickly kill any part of the plant they touch, but you may need to use multiple treatments throughout the season.
Chemical Application Best Practices:
Anytime you use chemicals treat weeds or algae, please keep in mind the following:
- Treat your pond in sections.
- Treat only half the pond’s surface at a time.
- During hot weather or when treating heavy growth, treat no more than a quarter of your pond at a time and wait the full 14 days before re-applying. This helps lower the risk of fish loss during hot weather or when treating heavy growth.
- Once the weeds have browned, use a rake to remove as much dead material as possible. This prevents an accumulation of dead plant material and muck.
