A watershed is the land area that drains rainfall and runoff into a water body, e.g. a dam, lake, river or reservoir. The quality of water in a water body is directly influenced by everything that happens within this watershed. Healthy watershed land leads to healthy water, while unhealthy land tends to lead to unhealthy water.
How to determine your watershed area
The two easiest ways to determine the size and boundaries of your watershed is to look at a topographic map or visually inspect the surrounding peaks from the water’s edge. You can also use GIS software if you have access to this.
- Topographic Maps – Use topographic maps with elevation data to identify the high points surrounding your dam or lake. These ridgelines define your watershed boundary.
- Visual Inspection – You can more roughly determine your watershed area by standing by your dam or lake and looking in each direction and making note of the surrounding peaks. The ridges between these peaks mark the watershed boundary.
- GIS & Online Tools – Geographic Information System (GIS) software or watershed mapping websites can provide precise watershed coordinates.
Once you have defined your watershed, you can assess potential risks and implement effective management strategies to improve water quality.
Factors that impact dam and lake water quality
Several factors within your watershed can significantly affect the health of your dam or lake. Understanding these influences can help you take action to prevent water quality issues such as algae blooms, sediment buildup and low oxygen levels.
1. Land use activities
- Agriculture – Fertiliser and manure runoff introduce excess nutrients to water bodies, particularly phosphorus and nitrogen, which can lead to excessive algae and aquatic weed growth.
- Residential developments – Lawns, septic systems and impervious surfaces (e.g. driveways, roofs, roads) contribute to stormwater runoff which can carry pollutants into water bodies.
- Forests & natural areas – Healthy forests and wetlands act as natural filters, reducing the amount of pollutants entering your dam or lake.
2. Erosion & sediment runoff
- Bare soil, overgrazed land and construction sites can lead to increased sediment entering the water, often making the water muddy and reducing water depth over time.
- Heavy rain events can accelerate erosion, washing more debris and nutrients into your dam.
- Different soil types impact water flow. For instance, sandy soils allow more infiltration, while clay-heavy soils increase runoff.
3. Nutrient loading & algal blooms
Excess nutrients from fertilisers, animal waste and decomposing vegetation can lead to an excess of nutrients in dams and lakes. These nutrients are food for aquatic pests such as harmful algal blooms (HABs), which deplete oxygen and threaten the lives of fish and other aquatic animals.
4. Pollutants & contaminants
- Pesticides, herbicides and industrial pollutants can enter dams and lakes through runoff, harming aquatic life.
- Bacteria from livestock or failing septic systems can also enter water bodies leading to unsafe water conditions.
Improving water quality through watershed management
Good watershed management can significantly enhance the health and longevity of your dam or lake. Here are some strategies to reduce pollution and improve water quality:
1. Buffer strips & vegetative barriers
- You can plant native grasses, shrubs and trees along shorelines and drainage areas to filter pollutants and reduce erosion. We recommend not planting trees too close to the water’s edge as their roots can cause erosion problems and leaf litter entering the water adds to the nutrient load, feeding algae and aquatic weeds.
- Wetlands act as natural filters, absorbing excess nutrients and trapping sediments. These can be particularly beneficial when located upstream in heavy water corridors. For instance in valleys where a lot of water comes through.
- You can also use silt curtains to prevent contaminated water mixing with fresh water.
2. Reduce nutrient runoff
- Minimise (or eliminate) fertiliser use on the watershed you’re trying to manage. If you do use fertilsers, use phosphorus-free chemicals and don’t use them close to the water body.
- Implement controlled grazing and manure management strategies to reduce agricultural runoff.
- Prevent leaves, grass clippings and organic debris from entering the water, as they contribute to nutrient loading when they decompose.
3. Control erosion and sedimentation
- Install silt fences and erosion control blankets on construction sites.
- Use cover crops and no-till farming to protect soil from erosion.
- Stabilise the banks of waterbodies by encouraging grasses or shrubs to grow in these areas and hold the soil in place.
- You can also line your dam to prevent erosion of banks. This has the added benefit of reducing ground seepage which helps maintain the water level.
4. Manage stormwater effectively
- Install rain gardens and retention basins to capture and filter runoff before it reaches your dam or lake.
- Steer away from non-penetrable surfaces where possible, e.g. use gravel on roads, permeable pavers or rain-absorbing landscaping techniques.
5. Monitor your water regularly
We don’t think it’s necessary to lab test your water, but we do recommend keeping an eye on your waterbody at different times of the day and season, and after extreme weather events, to see how it changes. You may even want to take photos to document changes. This can help you keep tabs on when the problems (e.g. aquatic weed, algae, foul smells) are occurring.
Treating muddy water
If you’re having problems with muddy water from inorganic material, e.g. dirt, soil etc, we first recommend you put plans in place to reduce soil erosion, e.g. plant vegetation on banks. After that you can use a flocculant like WaterTreats Clearwater Flocculant. This flocculant introduces an opposing ionic charge to the suspended particles causing them to clump together and sink to the bottom. At the right dosage, flocculant is safe for animals, plants and swimmers.
Treating algae and aquatic weeds
If you’re dealing with algae and/or aquatic weeds then you have excessive nutrients in your water. To help with this, work on strategies to reduce how much chemicals, manure and biological debris is entering your water. You can also reduce nutrients in your water through growing populations of “good” aerobic bacteria that live in your water column. At high enough numbers, these guys use all the nutrients for their own growth, which depletes what’s leftover for other creatures like algae and weeds.
Aeration and probiotics
You can increase aerobic bacteria populations in two ways: aeration and probiotics. For best results, use both methods in tandem. Aeration increases oxygen levels in the water which makes it easier for aerobic bacteria to grow. And probiotics provides these “good” (aerobic) bacteria with cultures, enzymes and trace nutrients to support their populations.
Treating smelly water
Anaerobic bacteria, aka ‘oxygen-hating’ bacteria, cause fowl and toxic smells as part of their metabolic processes. They emit odours like methane and hydrogen sulphides. Most of these smells are actually being produced by the bacteria as they slowly eat away at the sludge and suspended organic material. These guys are just a lot slower at breaking this stuff down than the “good” (aerobic) bacteria.
Aeration and probiotics
As above with treating algae and weeds, the best way to get rid of smells is to grow your populations of “good” aerobic bacteria so they steal all the resources and starve out the “bad” anaerobic bacteria. Aeration and probiotics does this by promoting growth of “good” bacteria that love oxygen and stacking the odds against “bad” bacteria that can’t survive in highly oxygenated environments.
Natural neutralising products
In a rush? While you wait for conditions to change, you can use an odour nuetralising product like DAZZeL Eco Plus. Derived from plant leaves and herbs, DAZZeL Eco Plus works by binding with odour causing molecules and breaking them down to nothing, thus removing the smell. This means DAZZeL Eco Plus doesn’t mask smells, but rather neutralises them for good—making it an ideal long-lasting solution to odour reduction.
Need advice on your watershed?
Contact us here and we’ll be happy to provide FREE advice.