Algae Boosting Phosphorus


Recently, much has been made about limiting the use of phosphorus. Some fertilizer brands have stopped adding phosphorus to their product and several states have banned the use of phosphorus in lawn fertilizer outright. If you haven’t heard by now phosphorus is like steroids for algae. It can cause large, harmful algae blooms in river systems and lakes.

But what does this mean in the scope of a small backyard pond or private lake? Before we understand what we can do, we first need to be conscious of the nutrient balance any body of water naturally contains.

Recipe for Disaster

Algae need just a few ingredients to grow, sunlight, CO2, water and a few organic nutrients. If you think about this, most of these ingredients are no brainers. Sunlight and CO2 are all around us; and water is the base of the pond system, obviously. The limiting factor of this recipe is the nutrients. Algal growth in fresh water is generally limited by phosphorus; therefore, phosphorus additions to fresh water create ideal conditions for a green, algal filled water system. Nitrogen is also a limiting nutrient but is more problematic in saltwater systems. Algae spores are in the air, so if conditions are favorable (all of the ingredients are present) algae growth will most likely occur.

But where is all this extra phosphorus coming from? The most common external sources are, leaves, grass clippings, rainwater runoff and waterfoul waste. Internal sources include fish waste and decaying organic matter in the bottom of the pond.

Nutrition Overload

Eutrophication is a form of water pollution caused by increased nutrient inputs to the water and subsequent increased biological productivity of the water. Nutrient additions to surface water stimulate excessive plant and algae growth. The algae tend to become the dominant species and therefore produce the majority of the water quality problems and choking out other life. As algae die, they sink to the lake or river bottom and decay. Their decay releases even more nutrients and further depletes the water of dissolved oxygen. This entire process is known as eutrophication and it continuously moves towards a hypereutrophic system with high nutrient levels and murky pond water.

Trophic Stage


Oligotrophic Clear waters with little organic matter or sediment and minimum biological activity
Mesotrophic Waters with more nutrients and, therefore, more biological productivity.
Eutrophic Waters extremely rich in nutrients, with high biological productivity. Some species may be choked out.
Hypereutrophic Murky, highly productive waters, closest to the wetlands status. Many clearwater species cannot survive.


How to get a handle on nutrients

If you suspect that your pond is suffering from a nutrient overload start off by testing the water for phosphate, nitrate, ammonia and pH. Test kits are relatively inexpensive and can give you a quick overview of the water chemistry in your pond. Better understanding the cause of water quality problems helps to better treat the problem. If your water quality problems are indeed caused by high phosphorus, treatments such as ALUM and all natural phosphate binder can be added. They both work in the same manner by binding to phosphorus at the molecular level and rendering the phosphorus content in the pond system unusable by algae and aquatic plants.

One ounce of prevention is worth a pound of cure

Yes, binding the nutrients in the water is an effective treatment, but still, this is treating a symptom of a larger problem. It is most important to keep external sources of phosphorus out of the pond system as much as possible. A proper filtration system should remove floating debris, not allowing additional organic matter enter the system. Care should be taken on larger earthen ponds and lakes to not letting grass clippings or other nutrient sources enter the water. New lined ponds should be constructed at a higher grade than the surrounding landscaping; this creates a buffer and prevents phosphorus and other runoff from contaminating the pond system. Furthermore, stop using phosphorus based fertilizers altogether. That’s the middle number in N-P-K (Nitrogen-Phosphorus-Potassium). For example, in a 12-4-8 blend, 4% of the weight of that fertilizer is phosphorus. That much nutrition content in a pond system can have disastrous effects.

It’s not all bad

Ponds with adequate but not excessive levels of phosphorus can actually be healthy biological systems. Plant and algae are important parts of a balanced ecosystem. Additionally, algae are the number one producer of dissolved oxygen in most ponds, the most important factor in a healthy body of water. So keep an eye on your pond chemistry. If you are seeing green, ask yourself, are there too many nutrients?