Lagoon Algae and Weed Control

Algaecide, herbicide and biocatalyst products for wastewater lagoons, including duckweed and watermeal control that respects your discharge permit.

Short answer

Algae and duckweed in a treatment lagoon block sunlight and surface reaeration, drive dissolved oxygen down, and turn into BOD load when they die. Control means an algaecide or aquatic herbicide paired with a biocatalyst that breaks down the dead material before it settles into the sludge blanket.

What we carry

Argos

Argos Lagoon Algaecide

For: an algae bloom blocking light and surface reaeration

Copper-based algaecide for wastewater lagoons, controlling filamentous, planktonic and blue-green algae. Tank mixed with a biocatalyst to handle the dead biomass.

$250Liquid, tank mixed

PondZilla

PondZilla Pro

For: an algaecide that is not working as well as it should

Enzyme-based biocatalyst that boosts algaecide and herbicide penetration in wastewater lagoons and degrades the dead plant material afterwards.

Quoted to your siteLiquid biocatalystFreight2 sizes

Duckweed Complete

For: a duckweed or watermeal blanket covering the cell

EPA-registered herbicide paired with a biocatalyst for duckweed and watermeal in wastewater lagoons. Case covers roughly five acres of surface treatment.

$1,500Herbicide plus biocatalyst, supplied as a case

Which one for which problem

Product	Reach for it when	Form	Applied from	Timeline
Argos Lagoon Algaecide	An algae bloom blocking light and surface reaeration	Liquid, tank mixed	Sprayed evenly over the target area	Days for die-off
PondZilla Pro	An algaecide that is not working as well as it should	Liquid biocatalyst	Tank mixed with the algaecide or herbicide	Applied with each treatment
Duckweed Complete	A duckweed or watermeal blanket covering the cell	Herbicide plus biocatalyst, supplied as a case	Sprayed over the surface, or subsurface	Days for die-off, weeks for breakdown

Plenty of systems run more than one of these. They are complementary far more often than they are alternatives, and each product page says which it pairs with and why.

Almost everything written about algae and duckweed control is written for private ponds. A treatment lagoon is a different animal: it discharges under a permit, and every pound of vegetation you kill and leave in the water becomes oxygen demand your cells have to treat. The vegetation guide covers the permit and infrastructure traps in full.

The two-part rule

Treating vegetation in a lagoon is always two jobs, and catalogs usually sell you only the first.

Kill it. A copper-based algaecide handles filamentous, planktonic and blue-green algae. An aquatic-labelled herbicide handles duckweed and watermeal.

Then deal with the biomass. Dead algae and plant matter sink. In a private pond that is an aesthetic issue; in a treatment cell it becomes BOD and TSS inside your own treatment train, and it settles into the sludge blanket you are probably already managing. A biocatalyst applied with the kill accelerates that breakdown so the material degrades in the water column rather than banking on the bottom.

Problem	Product	What it does
Filamentous, planktonic or blue-green algae	Argos Lagoon Algaecide	Copper-based algaecide, fast die-off
Duckweed and watermeal	Duckweed Complete	EPA-registered herbicide plus biocatalyst
Dead biomass after any treatment	PondZilla Pro	Biocatalyst, penetration and breakdown

Treat in sections

A whole-surface kill on a loaded cell puts the entire decay load into your treatment train at once. Treat in sections sized to your cells’ oxygen budget, and schedule around discharge events. That single discipline prevents most of the self-inflicted permit trouble that follows a vegetation treatment.

And read the recurrence

If algae or duckweed keeps returning, it is a loading and mixing diagnostic rather than a housekeeping chore. Duckweed cannot establish on moving water, and a cell wearing a complete blanket has told you it is nutrient-heavy and under-mixed. The durable answer is usually aeration, with chemical control clearing what is already there.

Common questions

Why pair an algaecide with an adjuvant?

Two reasons. The adjuvant helps the algaecide penetrate the protective slime layer around algae cells, so the treatment actually works, and it accelerates breakdown of the dead material afterwards so it does not settle out and add to your sludge blanket. Killing algae without handling the biomass just moves the problem to the bottom of the cell.

Do I need a permit to apply these?

Often yes. Pesticide applications to waters, including treatment lagoons in many circumstances, can require coverage under your state's Pesticide General Permit, a licensed applicator, or both. Confirm with your state environmental agency before you spray anything. The product label is law and your state rules sit on top of it.

Will treating algae hurt my treatment biology?

The biocatalyst products are formulated not to harm beneficial bacteria. The larger risk is the decay load: a large kill releases organic material into a cell that then has to treat it. Treat in sections sized to your cells' oxygen budget rather than the whole surface at once.

Why does duckweed keep coming back?

Because it is a symptom. Duckweed thrives on nutrient-rich, still water, so a cell that keeps growing a blanket is telling you it is nutrient-heavy and under-mixed. Herbicide clears the current mat; aeration and loading control are what stop it returning.

Read before you buy

Vegetation