Black Muck also referred to as organic sediments accumulates on the bottom of the pond but mostly on the sloping side walls. As ponds mature the percentage of black muck increases to the point of becoming a problem. Leaves form deciduous trees, branches, dead plants and expired critters are examples of slow to decompose organic materials that promote anaerobic conditions and release nutrients (P, N, CO2, NH3). To sound more scientific we will call this Labile Organic Matter.  LOC provides the aquatic ecosystem with a source of organic carbon that is essential for the support and growth of heterotrophic  bacteria, the real custodians of the pond bottom. Too much organic matter causes a problem for these environmental workers, they can’t keep up and may require overtime pay.

Here’s our recommendations to keep your pond water healthy:

  • Determine how much black muck is on the pond bottom and side walls by stirring up the bottom with a rake or shovel. You can use a core sampler if available.  If the sediments come to the surface as a black cloud with lots of gas bubbles and smells like rotten eggs you should consider reducing this material down to a layer of less than two inches with the right type of probiotic bacteria. Watch for lost dog and kid toys when you do this.
  • Examine the black muck for small animals and insects. Snails, red blood worms and leeches live in organic sediments that have relatively low dissolved oxygen (anaerobic conditions). Stone flies, dragon fly larva, tadpoles and small fish usually indicate better sediment conditions (aerobic conditions). You may consider installing an aeration system to reduce the anaerobic conditions.
  •  Draining the pond for several weeks will expose black muck to more sunlight and oxygen to facilitate decomposition. Old mature ponds may need to be drained and cleaned out with excavation equipment.  This is a drastic approach but you essentially end up with a new pond.

You will get more enjoyment having a pond with less organic sediments (black muck) because the water conditions will be better, the pond critters will be happy and no one will be pulling leeches off after swimming.