Weed and Algae Management for Ponds and Lakes

Weed and algae management for ponds and lakes can be tricky. Please realize that every pond is different, and strategies should be adjusted as conditions change. So, you should use these basic strategies as a reference or example, not as a strict plan to follow regardless of the situation. Also, many of these techniques can and do impact oxygen levels in ponds. Even ponds with aeration systems can experience oxygen depletion and fish kills under extreme conditions, such as very heavy weed or algae growth. However, when applied properly, these products are safe and effective and can actually help the environment more than they hurt it by improving aquatic conditions and eliminating invasive exotic species. You should always read and follow product label instructions when applying these products. Finally, laws vary from state to state regarding application of these products. If you are unsure, you should contact your states Department of Natural Resources or like agency.

Filamentous Algae Control for Natural Ponds and Lakes

  1. (Optional) Apply a Pond Dye early in season before Algae begins growing.
  2. Control external nutrient loading. For example, if you fertilize your yard, either quit or use a zero phosphorous fertilizer (middle number needs to be zero e.g. 10-0-10). Also, keep leaves, grass clippings, surface water runoff, soil erosion (especially shorelines) & animal waste (e.g. geese & farm animals in watershed area) out of pond water.
  3. Install a properly sized Aeration System that brings oxygen to the bottom in the deepest water during summer. A general rule is to turn over the entire water volume once every 24 hours.
  4. If your algae is not too severe and you want to treat the entire pond, apply EarthTec Algaecide at the lowest recommended rate, which is 0.8 gallons per acre foot of water.  If control is not achieved within 2 weeks, reapply.  If you have severe growth of algae, we recommend treating small parts of your pond at a time (not more than 1/4 of your pond) by spraying Cutrine Plus Liquid Algaecide directly over the treatment area.  Mix about 13 or 14 oz Cutrine Plus into a gallon of water and spray directly onto the algae where you see it. Adding a Surfactant (approximately 2 or 3 ounces per gallon of spray mix) greatly increases effectiveness, as does applying on sunny days when the water temp is over 60F.  If you have dense mats of algae on the surface, we recommend breaking them up first before spraying with an algaecide.  For resistant strains you may need to add other products, such as Reward. We recommend asking for assistance before proceeding with this step. Do not exceed 1.2 gallons of Cutrine Plus per acre foot of water per month. Warning! – Decaying algae or weeds lead to oxygen depletion, which can cause fish kills. Always read and follow product labels, as Keystone Hatcheries provides this information for your convenience only and accepts no liability for issues caused by treatments.
  5. Apply Phosphorous Binder/Remover after algae has been treated to tie up phosphorous released from decaying algae. This greatly reduces the nutrient levels of the pond.
  6. Apply Pond Bacteria to improve water quality and digest organic matter on the bottom. Follow product instructions and start treatments in the spring when water temps reach 55F and apply until fall when water temps drop below 55F. Please note that Pond Bacteria applications are more effective if the water is warm and well aerated.

    Submerged Aquatic Weeds

    1. Identify weeds, including problem and non-problem species.
    2. Apply a Pond Dye early in the season before weeds proliferate.
    3. If you identify Eurasian Watermilfoil or Curly-leaf Pondweed, apply Sonar at 30ppb (about 2-1/2 ounces per acre-foot of water) in ponds with little or no flow early in the spring before weed has a chance to proliferate. It can be diluted in a 5 gallon bucket of water and spread around the pond or sprayed evenly over the surface.
    4. If you identify Coontail, native Watermilfoil or native Pondweed species, spot treat only in areas that the weeds are interfering with your water use by applying Hydrothol at the rate recommended on the label. Warning! - Never treat more than 10% of your pond at a time with this product. Hydrothol’s half life is 7 days, so limit applications to 10% of pond area per week. An alternative treatment is to spray Reward at the rate of 2 gallons per surface acre over areas that you wish to control the vegetation.
    5. Consider removing live or dead aquatic vegetation with an Aquatic Rake or Cutter to reduce the amount of decaying organic matter in the pond, which will reduce the nutrient level.

    Duckweed & Watermeal

    1. Control nutrients as described under #1 for Algae.
    2. If you have a “small” pond, consider physically removing the Duckweed &/or Watermeal with a Duckweed Seine.
    3. Create motion in the water to deter regrowth with an Aerating Fountain or Surface Aerator.
    4. If there is no desirable vegetation in the pond that you wish to keep, you can apply Propeller at the rate of 6 to 12 ounces per surface acre, along with a Surfactant. Product should be diluted with enough water to facilitate even distribution via sprayer over the Duckweed & Watermeal.

    Cattails and Water Lilies

    1. Wait until Cattail seed heads appear or Water Lilies blossom, but before first frost.
    2. Mix 3 oz of Shore-Klear or AquaNeat with 3 oz of Surfactant in 1 gallon of water and spray evenly over foliage that is out of the water.
    3. Wait at least 2 weeks before removing dead vegetation to allow herbicide to penetrate to roots.
    For more information about weed and algae management for ponds and lakes, please contact us.