Illustration for Cleaning a Dock or Seawall Without Polluting the Lake

The usual house-wash mix is the wrong tool here, and a good washer should say so before you do. Lakefront owners ask how to get the green film off a dock or lift. Pressure washing forums ask the same thing from the other side. In one thread about an aluminum dock, the first reply suggested a bleach mix. The next warned that strong acids and alkalis, including bleach, can etch aluminum. Another reply simply said to keep the fish happy.

Why house-wash mix doesn’t belong on a dock

Many house washes use sodium hypochlorite, the active ingredient in bleach. Its EPA-registered labels can be blunt. For one bleach product, EPA told the maker to state, “This pesticide is toxic to fish and aquatic organisms.” The same statement says not to discharge effluent containing it into lakes, streams or ponds. The exception is when a federal discharge (NPDES) permit allows it and the permitting authority was told in writing first. That label also warns that prolonged contact with metal may cause pitting or discoloration.

That permit system comes from the Clean Water Act. EPA explains that the act bars anyone from discharging pollutants through a “point source” into US waters without an NPDES permit. It defines a point source broadly, from a pipe to a ditch or channel. A Michigan Sea Grant course for marinas says the same thing in plain terms. Even when washing a boat hull with a garden hose, a permit is still required if the wash water heads toward the lake.

We’re not lawyers, and this isn’t legal advice. What counts as a discharge on your shoreline is a question for your state’s natural resources or environmental agency. The safe default is simple. Don’t put anything on the dock that you wouldn’t want in the water.

Dock makers agree. One says to avoid bleach, ammonia and petroleum-based solvents. It says to pick cleaners that are biodegradable, phosphate-free and close to neutral pH. Another lists chlorine bleach, phosphates, ammonia and disinfectants as things to skip. They can feed algae blooms and pull oxygen from the water. EPA’s handbook for marinas and boaters makes the same point about cleaning products that contain chlorine or phosphates.

How to clean each part

Surface Start with Watch out for
Aluminum dock or lift frame Mild soap, soft brush, low to moderate pressure, wide nozzle Bleach, ammonia and abrasive powders can etch it
Wood dock Soft brush and light pressure Pressure washing can splinter the surface
Plastic floating dock Soap and water with a soft brush, then a rinse Chlorine bleach, phosphates, disinfectants
Concrete dock or seawall Brush and plain water first Cleaner runoff straight into the lake

Aluminum. One dock maker suggests mild biodegradable soap in warm water. For tougher stains, it suggests diluted white vinegar or a gentle marine cleaner. It says aluminum takes pressure on a low to moderate setting with a wide nozzle. Add a brush on stubborn spots.

Wood. A floating-dock maker warns that pressure can splinter wood decking. Are the boards going gray before a reseal? Our deck prep guide covers cleaning, brightening and drying before stain. Some steps there use chemicals. On a dock, check the label for water warnings first. For plastic decking boards, see composite deck cleaning.

Concrete docks and seawalls. The runoff problem is the same as on any dock. Without a cleaner, some growth will stay behind. Our water-only wash guide explains why. On a seawall, that may be the trade-off you accept.

Boat lifts. Washers in one thread said the practical way to reach every side of a lift is from a boat. Brush off the algae by hand, then rinse on low pressure. One added that the job’s price should reflect the risk of working over water.

Moving a dock or lift

Wisconsin has about 15,000 lakes. Its DNR asks everyone to inspect boats and equipment, remove any attached plants or animals, and drain all water. Its guidance even advises against chemical decontamination of wake boats. Part of the concern is chemicals discharged into the environment.

Next door, Minnesota’s rule is stricter for shoreline gear. The Minnesota DNR says docks and lifts must stay out of the water for at least 21 days before they go into another lake. That’s state law. It also says hauling a dock or lift with zebra mussels attached to another site for decontamination needs a free permit. If you’re buying a used lift, check its posts, footings and wheels.

What to ask before you hire

  • What will you spray, and where does it go? “Water and a brush” is a good answer, and so is a named biodegradable soap. “Our regular house mix” is not.
  • Will you work from a boat or the shore? Ask how they reach a lift without standing on it.
  • Who checks the rules? A careful washer knows to ask the state agency before spraying any cleaner over water.

The rest of the call, including insurance, is in our questions to ask a house washing company. If birds are the mess on your dock, see bird droppings on pavers, stucco and docks. Here’s how we check every claim: our methodology.

Sources

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