Potential Environmental Impacts of Retention Ponds

Any pond you add to a natural or developed landscape should enrich the ecosystem by treating runoff and offering a habitat for wildlife. Even a carefully designed retention pond can turn from a positive part of the environment into a negative one when neglected. Retention ponds require regular maintenance, even when designed to process waste and thrive without constant attention. If you undersize your retention pond or forget to keep it dredged and inspected, it could end up damaging the local environment in one of the following ways.

Overflow and Flooding

Undersized retention ponds will eventually flood when an unexpected amount of rainfall occurs. Even if you’re building a storm water system in an area with low annual rainfall amounts, the region will eventually experience a serious flood that could overwhelm the pond’s banks. Flooding ponds damage the surrounding soil and waterways in addition to causing erosion and Property damage can also occur if the water reaches nearby structures. Oversized retention ponds are far safer and more reliable than basins built exactly to minimal specifications for your area’s rainfall averages.

Soil Collapse and Saturation

Even if the pond is large enough to hold flood waters without any surges over the banks, long-term seepage of water through the soil can destabilize the system. It’s easy for soil to become so saturated with water that it collapses dramatically, creating large voids or sinkholes under and around the retention pond. Impermeable and permanent liners like buried geomembranes are the best way to prevent seepage and keep soils stable underneath and around the pond.

Mosquitoes and Other Insects

Still, shallow, and warm water serve as the ideal breeding ground for mosquitoes and other nuisance insects. Mosquitoes can pose serious public health risks by spreading human and animal diseases. Even in areas where the insects don’t carry any serious diseases, they’re annoying and make it hard for nearby residents to enjoy the outdoors. Shade, proper water depth, hungry fish, and water surface disturbances all interrupt larvae growth and control insects naturally. Mosquito fish are a good choice for ponds in warm climates, but there are also hungry panfish and bluegill varieties for every climate that can keep mosquito larvae under control. For widespread insect problems, fish and plant-safe chemicals are available to interrupt the life cycles of the insects.

Drowning Risks for Animals

Like all other ponds commonly installed in the borders between developed and undeveloped land, retention ponds can attract wildlife and feral animals living near homes. While many birds and small animals can safely drink from the pond without issue, larger livestock and wildlife may become mired in mud or stumble on slick banks and drown in the water. Drowned animals are a health hazard and are upsetting for residents living near a neighborhood retention pond. Shallow and gradual banks, that are planted and not made from bare concrete, allow all animals to safely access the water. If you must build steep or slick banks, consider fencing to keep pets and wild animals alike from falling in and getting injured or trapped.

Erosion and Bank Scouring

When water enters the retention pond from the surrounding ground or bare ditches, the water’s volume and velocity can trigger erosion that dumps extra silt into the bottom of the pond. Rapid filling and emptying of the pond also increases the chance of bank scouring that leads to fragile overhanging edges that collapse into the pond. Erosion and bank scouring quickly fills the bottom of the pond with sediment, reducing its volume and increasing the chances of mosquito issues. Careful design and preparation of feeder ditches and drains is essential to minimize these soil-related issues.

High Pollutant Levels

Minimizing the amount of water entering a retention pond actually makes it harder to maintain a healthy ecosystem. If pollutant levels rise because there’s not enough water to dilute the mixture, the processes that treat the water will slow down or stop entirely. Healthy bacterial colonies thrive when there’s enough retained water in the pond along with new water entering during storms to balance the nutrient and chemical levels. Directing a larger surface area to a particular body of water can increase dilution and keep water safe for fish and plant life.

If you’re experiencing any of these issues with your existing retention ponds, it’s never too late to overhaul the basin and improve its performance. Emptying out the pond, reshaping it for the appropriate volume, and adding a flexible liner can turn an environmental hazard into a thriving and healthy pond that improves the area.


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