Perhaps nothing is more frustrating than finally building the pond or lake of your life only to find it doesn’t hold water. Just as frustrating are unsupported repairs and repair theories.

We will focus our leak location and repair strategies in 2 main areas: 1) SYNTHETIC LINED WATERSHED, from small garden ponds to multi-acre ponds and lakes. 2) NATURAL LINED BASINS – These can be excavated ponds or lakes without a dam embankment or a pond or lake built with a dam.

First things first: how is the leak located? This can be exceptionally simple or painfully difficult depending on the situation. Let’s state the obvious and move on from there – look for the wet spots around the pond. A soil probe will allow you to find moisture below the surface. If you don’t have access to a soil probe, a trench shovel will work just fine. Explore or dig as deep as you can into the suspicious area and examine the soil for moisture content. The best time to look for wet areas around the pond is after a prolonged dry period, preferably a week or more. If you find a lot of moisture, you are likely near the leak and may narrow your search. Pay attention to the vegetation around the pond. Lush green vegetation during prolonged dry spells can also help you narrow down your search.

Once you have narrowed down your search or if you just can’t narrow down your search, let the surface of the pond water drop without replenishing the water until the water level stabilizes. Mark this level and investigate the pond around this elevation. For a synthetic liner pond, you have found the elevation of the leak, a careful inspection of the liner at this height should allow you to find the leak.

If you have an EPDM rubber liner (Firestone Pondgard or similar), the repair is pretty simple once you’ve found the leak. Purchase an inexpensive EPDM repair kit and apply according to instructions. If this is the only leak in your pond, you can fill up and enjoy!

If the pond is a natural bottom or an unlined pond, the search becomes a bit more complex. As with the lined pond, it is worth examining the pond at the elevation where the water level stabilized. There are 2 reasons why the water level may have stabilized at this level. One, this is the elevation of the leak or two, this is the natural elevation of the groundwater (water table). A simple test of the pump will determine with reasonable certainty if the bottom of the pond has intercepted and is connected to the water table.

To perform the pump test, select a pump that will allow you to remove approximately 6 inches of water from the surface of the pond in less than 3 hours. Mark the initial water surface elevation and the final water surface elevation. For the next 6-8 hours, carefully monitor the surface of the water. If the water surface bounces back towards the starting point, the pond has most likely intercepted the water table. If the water surface remains at the same elevation, the initial elevation of the water surface is the elevation of the leak.

Now that the leak has been located or at least the location has been narrowed down, it is time to review your options for repairing the leak.

First, let’s dispel a common misconception. It is VERY unlikely that spraying a modest or even substantial amount of bentonite in any of its various commercial forms into standing water will stop or slow a leak. Bentonite is an expanding clay found in Wyoming that plays a role in repairing leaks and sealing bodies of water. It is certainly a great product when used correctly.

To properly apply bentonite to seal a pond, the pond must be drained and then the bentonite must be incorporated into the soil at the bottom and sides of the pond. The bentonite application rate ranges from 2 pounds to more than 5 pounds per square foot, depending on the characteristics of the soil. For clay and loamy soils, 2 pounds per square foot MAY be sufficient. For sandy soils, 4 pounds MAY be sufficient and for soils containing gravel and rock, more than 5 pounds will be required to obtain a seal. Once the bentonite is applied, the soil must be raked with discs to mix the soil and bentonite and then compacted.

For a leaky embankment, if the location of the leak has been identified, it may be possible to construct a central trench in the embankment to reduce the leak. To install a center trench, dig a minimum 12-inch wide trench 3 feet below the elevation of the pond bottom. The trench should be located as far from the edge of the pond as possible while remaining on the flat top of the embankment. The objective is to create a waterproof core in the embankment that does not allow the passage of water. This waterproof core can be created in a number of ways. Bentonite can be mixed with excavated soil in a proportion of 30% bentonite and 70% native soil. The material should be put back into the trench and compacted with a trench roller, hammer, or excavator bucket at 6-inch elevations. Alternatively, the EPDM liner can be buried in the embankment by laying a solid sheet of EPDM liner along the wall of the trench closest to the pond and carefully backfilling the trench. Again, the soil must be compacted as the trench is filled in. Applying a bentonite mixture to the bottom of the siding curtain and the ends of the siding curtain will help prevent water from seeping around the curtain.

Another common place for leaks is along the pipes that penetrate the pond embankment. All pipes running through the pond embankment must be fitted with a dust collar to prevent water from flowing along the pipe. If a pipe is installed through the embankment without an antiseep collar, the pipe can be dug out and a bentonite plug installed around the pipe. Ideally, the bentonite plug should extend at least 3 times the diameter of the pipe around the pipe.