A Good Pond Gone Bad?

People often ask me about ponds they think are “dying,” or better yet—have “gone bad.” Of course, what they’re really referring to is a pond becoming increasingly nutrient-laden or eutrophic. These ponds become more and more shallow, and more and more vegetation grows both in and around the pond.

However, these ponds aren’t dying or “going bad.” The ponds’ owners may not like the way their ponds look, but there is nothing wrong with them. They’re simply aging. And that, unfortunately, is something we all go through!

Given enough time, all ponds will eventually fill in with vegetation and turn into marshes. The time needed depends on the pond and its location. Some ponds last 50 years or more, while others fill in within a few years of being built. However, for every pond, the aging process is inevitable.

So, how does a pond owner slow down the aging process? Most pond owners would like their pond to stay looking like a pond indefinitely. After all, who wants to build a pond just to have their investment turn into mud and cattails?

The most important thing a pond owner can do to prevent excessive growth of weeds and vegetation in a pond is to control (stop) the inflow of nutrients to the pond. Like land plants, growing aquatic vegetation needs nitrogen, phosphorus and potassium, along with various micronutrients. It is a simple fact of nature that where there are nutrients, soil and water, plants will grow.

Common nutrient sources for ponds include lawn fertilizer, manure from livestock and/or wild birds and animals, fallen leaves, leaking septic systems, and bare soil. Be sure to consider what's taking place upstream and uphill from your pond, as well as on your own land.

Unfortunately, people often find they have no control over the nutrient source. For example, this can happen when there’s an upstream nutrient source, or when the pond itself is the nutrient source.

Many ponds built by the USDA Soil Conservation Service (SCS) in the 1960s and 1970s are now much shallower because of the 30-plus years’ accumulation of leaves and sediment. These ponds are now huge, wet compost piles. The only real remedy for a pond like this is to have it dredged. For a maintenance dredge, a permit is needed from the Wetlands Bureau of the NH Department of Environmental Services (271-1969). Your county Conservation District can help you with the permit application, as well as provide you with a list of excavators in your area.

Luckily, most ponds don’t have that much muck on the bottom and aren’t completely overloaded with nutrients. For these ponds, I remind people that where there are nutrients, there is vegetation. This means you need to think about which aquatic plants you like the most, or for some people, which plants they hate the least.

Aquatic vegetation can be roughly divided into two groups. There are the macrophytes, a higher order plant that look like, well … plants! The other group is the algae, the green slimy stuff that slips through your fingers. Algae can spread quickly, and can form floating mats of dead or dying material, commonly referred to as pond scums. I have to admit, a pond covered with slimy mats of brown, dying algae truly does appear to be “going bad.”

Macrophytes commonly found in New Hampshire ponds include cattails, pickerel weed, water lilies, duckweed and rushes, along with submerged plants like coontail and bladderwort. All these plants compete with algae for nutrients. There are also several plants with attractive flowers and/or wildlife value that can be planted at the edge of your pond. Both Blue Flag iris and Cardinal Flower make beautiful, colorful additions. Shrubs are particularly good at taking up excess nutrients. Native shrubs that also help provide food for wildlife include buttonbush, nannyberry, wild grape and winterberry holly.

Good sources for these plants include your county Conservation District (many have spring plant sales) and the NH State Forest Nursery , which sells many native plants, and even has a special wetlands package.

By J-J Newman, UNH Cooperative Extension Aquaculture Specialist