Biological Lake Weed Control

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Biological lake weed control involves introducing a species into the lake to destroy the weeds. At the present, there are only a few biological controls available to the lake manager, and they have their drawbacks. Biological controls are popular because they do not involve chemicals, and are perceived as being “earth friendly”, but this may not in fact be the case.

Problems with biological lake weed control

Remember, that the need for the control is probably because a non native species was introduced into the mix to begin with, introducing another to control the first hardly seems wise.

In cases where the “grass carp” has been introduced into environments other than it’s native habitat, the results have been mixed, ranging from achieving the desired control, to lakes completely devoid of vegetation and almost all other forms of aquatic life. Other issues are escape, which can produce disastrous results downstream, and the potential for the accidental release of non sterile, reproductive capable grass carp into the environment.

There are a few other biological controls available. Basically, these are “bugs” that dine on specific species. The same issues exist with them as with the grass carp.

In general, we do not recommend the use of biological control measures for these reasons.

A better form of biological lake weed control

Natural, native biological control can be used safely by simply following good cultural practices for your pond or lake. This simply involves providing for proper pH, proper fertility, and then allowing nature to do the rest. A properly fertilized pond or lake will produce the right amount of phytoplankton to keep the water tinted, and the weeds at bay, as well as producing healthy fish.

See also: How To Fertilize A Pond Or Lake

Pond and Lake maintenance using Diatom Algae

Pond and Lake maintenance using Diatom Algae

By: Bhaskar M V


Water pollution issues in ponds and lakes and solutions to these problems are in the news now a days for all the wrong reasons. Water pollution is increasing due to human activity – increasing population and consumption has resulted in more waste being generated – sewage, fertilizer run off, etc. These enter ponds, lakes, rivers, estuaries, etc., and cause algal blooms leading to low dissolved oxygen problems and fish kills and dead zones. The main source of ‘pollution’ of water is nutrients – Nitrogen and Phosphorus from sewage and fertilizer. Industrial pollutants though more toxic and harmful are a smaller problem in terms of volume. Farmers use fertilizer since plants require them, fertilizers cause higher plant growth and this is a good thing. Why are these fertilizers regarded as ‘pollutants’ when they enter a waterbody? What type of ‘plants’ grow in the water due to these nutrients? Micro algae i.e., Cyanobacteria, Green Algae, Dinoflagellates, Diatoms; macro algae, aquatic weeds, are the various plants that can grow in water. The problem arises when the balance shifts in favor of one group and this dominates the water. Thus when there is a large bloom of Cyanobacteria or Dinoflagellates the water turns Green or Red and some of these species release toxins too. Water hyacinth or Duck weed too can bloom and cover the pond or lake. Which is the best species / group of ‘plants’ to grow in water? How to maintain the desired ecological balance of various species? We believe that Diatom Algae are the best group of micro algae to grow, they are the best food for fish and hence do not accumulate in the water. Cyanobacteria / Blue Green Algae, Dinoflagellates, water hyacinth, etc. are not consumed by zooplankton, fish, etc. and hence accumulate in water and become a nuisance and have to be removed by artificial means – physically removed or by use of algaecides and weedicides. Diatoms on the other hand are removed naturally by Zooplankton and fish. Catching fish is easier and more profitable than harvesting algae. Diatoms typically dominate water during spring, early summer and winter. Late summer is when Cyanobacteria and Dinoflagellates bloom and dominate the water. The reason for this is that Diatoms require more inputs than other micro algae, they are the most recent of the micro algae to have evolved – less than 300 million years ago. Cyanobacteria evolved more than 3000 million years and Dinoflagellates about 1000 million years ago. Thus Diatoms are the more complex of all micro algae and they require many micro nutrients and Silica to bloom. Iron, Manganese, Zinc, etc., are the micro nutrients require by Diatoms. These and Silica do not dissolve easily in water. Metals oxidize in water and silica (sand) is not by nature soluble. Thus these elements are the first to be exhausted in water leading to the end of Diatom bloom in early summer and consequent domination by Cyanobacteria. Thus is supply of silica and micro nutrients is increased the Diatom bloom can be prolonged and the bloom of other algae and weeds controlled. N P K are the inputs that are common to all plants and algae, thus when these are consumed by Diatoms other plants are starved out. However, since Diatoms are grazed upon by Zooplankton and fish their population is regulated naturally and the bloom will not get out of hand if adequate number of fish are available and if the silica micro nutrient supply is regulated. Thus the natural ecological balance can be restored and maintained throughout the year. A solution to provide silica and micro nutrients in water in a stable manner has been invented by Mr T Sampath Kumar of Bangalore, India. He researched for over 10 years from 1994 to 2004 and perfected the formula. Its now patented and marketed under the name Nualgi [NUtrition for Algae] . Nano silica is used as a base for delivery of all the micro nutrients. Nano silica disperses in water and does not dissolve, however the dispersed nano particles behave in the same manner as dissolved particles. The silica keeps the metals stable in water and prevents them from oxidizing. Thus metals in Nualgi are stable in water for a long time and they are bioavailable to the Diatoms. The maximum dosage of Nualgi is 0.25 ppm i.e., about 1 kg in 1 acre of pond 1 meter deep. The Diatom bloom lasts for about a week, so repeat doses have to be given weekly. The cost of Nualgi used is fully recovered from sale of fish. 1 kg of Nualgi results in 100 to 200 kgs of Diatom biomass. This results in 10 to 50 kgs of fish biomass. 100 kgs of Diatoms give about 100 kgs of oxygen and absorb 137.5 kgs of CO2. Diatoms bloom rapidly and the color of water changes from green to light brown in a few days. When Nualgi is used in a pond with a massive Blue Green Algae bloom the BGA may crash within hours of the first dose. Nualgi is thus a safe and economical alternative to mechanical aerators, algaecides, dyes, etc. Bhaskar

How To Fertilize A Pond Or Lake


So, you have had a few problems with your pond or lake that seem to indicate that you need a little extra fertility. Maybe what tipped you off was:

  • Poor fishing
  • Skinny fish
  • Low fish population
  • Excessive pond algae like blanket weed or pond scum
  • Excessive lake weed growth

Whatever it was that tipped you off, you have come to the conclusion that something has to be done to increase fish production, get rid of lake weeds and pond scum, and prevent these problems in the future.

  • You have done your homework.
  • You have tested the water clarity of your lake and solved any problems related to soil particles in the water.
  • You have checked the pH and corrected it if needed.
  • You have water which is too clear to support aquatic life, so you know that you need to produce algae bloom, and you know that that means you need to fertilize your lake.

How do you fertilize a pond or lake?

There are several suitable methods for pond and lake fertilization, but let me start off with a few cautionary statements.

Liquid pond fertilizer

Liquid fertilizer should be mixed with water before being applied to a lake or pond. The liquid fertilizer will be heavier than the water it is being applied to, and will sink to the bottom where it will probably either be neutralized, or initiate unwanted plant growth.

Keep fertilizer clear of outflow

If you are using buckets or platforms suspended in the water to slowly dissolve fertilizer, make sure that they are not close to your spillway or drain pipe. This could result in the majority of your fertilizer ending up downstream.

Simple pond fertilizer method

If you are using fertilizer in plastic bags, you can lay the bag in shallow water, 2 to 3 feet deep, and slit the top lengthwise and across to allow the fertilizer to dissolve.

Fertilizer platform

If you are using a submerged platform, the platform should be about 1 to 2 feet below the surface of the water, and the proper amount of granular fertilizer can be dumped onto the platform and allowed to dissolve at it’s own rate.

Fertilizer in a bucket

The same result can be attained by suspending a 5 gallon bucket full of fertilizer with small holes drilled into the sides from a dock. be sure that it is one to 2 feet deep.

Fertilizer products formulated for ponds and lakes

There are a lot of newer fertilizer products on the market specifically designed for pond and lake fertilization that offer other options such as finely ground granules. These products come with instructions and label directions.

Special aquatic weed control note:

It is important to start fertilization early in the spring. If algae bloom is in place before weeds and filamentous pond algae have a chance to get started, this will decrease the amount of weed control needed for the pond. See also: Lake Fertilization