CHAPTER 3 — Meet the Aquatic Weeds

Meet the Aquatic Weeds — Knowing What You Have Is Half the Solution

3.1 Name It Before You Treat It

When a dam becomes overgrown, the instinct is to act quickly. But the right response depends entirely on what is actually growing. Floating algae, a carpet of duckweed, a raft of water hyacinth and a submerged tangle of hornwort look different, behave differently and reach the water in different ways.

What they share is the reason they thrive: an excess of nutrients in the water, as Chapter 2 explained. Identifying the growth does not change that root cause — but it does tell you what you are looking at, how it spreads, and what to expect as balance is restored.

3.2 Algae — The Microscopic Multitude

Algae are simple, plant-like organisms that live suspended in the water or form mats on the surface and along the edges. Most are microscopic, but in their millions they colour the whole dam green, as covered in the previous chapter.

Some algae stay dispersed through the water, turning it opaque. Others — the filamentous kinds — form long green threads that tangle into floating mats, often described as blanket weed. Both respond very fast to warmth, light and available nutrients, which is why an algal bloom can appear within days.

3.3 Duckweed — The Green Carpet

Duckweed is a tiny free-floating plant, each one only a few millimetres across, with small trailing roots. Individually it is easy to overlook. Collectively it can cover an entire surface in a bright green carpet so complete that the water beneath disappears from view.

Duckweed spreads by simple division — each plant splits into more — so a light scattering can become a full cover in a matter of weeks under warm, nutrient-rich conditions. Because it sits on the surface, it blocks light from reaching the water below and slows the movement of oxygen between air and water.

3.4 Water Hyacinth — The Floating Invader

Water hyacinth is a much larger free-floating plant, with glossy leaves, a bulbous stem and, at times, an attractive purple flower. That appearance is deceptive. It is one of the fastest-spreading aquatic plants in the world and is regarded as a serious invasive species across much of southern Africa.

Under favourable conditions a hyacinth population can double in size in a matter of days, forming dense floating rafts thick enough to walk on in places. These rafts block light, restrict boat and water access, and greatly increase water loss through the leaves. Where hyacinth takes hold, it changes the whole character of a water body.

3.5 Hornwort — The Submerged Tangle

Hornwort is different again. Rather than floating on top, it grows beneath the surface as long, branching, feathery stems that form dense underwater masses. It has no true roots and takes up nutrients directly from the water along its whole length.

Because it grows out of sight, hornwort is often noticed only once it has filled much of the water column, tangling nets, lines and pumps and making the water difficult to use. Like the others, it flourishes where nutrients are plentiful and light can still reach it.

3.6 Different Plants, One Root Cause

These four types of growth look nothing alike. One is microscopic and suspended, one carpets the surface, one forms towering floating rafts, and one fills the water from below. Yet every one of them is driven by the same thing: an excess of nutrients, principally nitrogen and phosphorus, accumulating faster than the pond's biology can draw them down.

This is why identifying the plant matters for knowing what you are dealing with, but does not change the fundamental approach. Removing the visible growth — skimming algae, raking hornwort, hauling out hyacinth — leaves the nutrients behind, and the growth returns. Lasting control comes from addressing the nutrient surplus that feeds all of them.

3.7 Practical Application — Working on the Cause

Whichever plant has taken hold, the biological approach is the same: reduce the nutrients that fuel the growth rather than chasing the growth itself.

AquaDigest® introduces beneficial bacterial cultures — multiple naturally occurring Bacillus species — that draw down the excess nitrogen and phosphorus in the water and accelerate the natural decomposition of the nutrient-rich sludge on the pond floor that continually feeds new growth. As the available nutrients fall, conditions become less favourable for algae and aquatic weeds, and the water can move back towards a clearer, more balanced state.

Because this works by shifting the pond's underlying balance rather than removing what can be seen, it follows the pond's own biological pace. Where growth is heavy, physical removal of the bulk of the material can still play a role alongside the biological programme, which then works to keep it from returning. Chapter 8 sets out how a treatment programme is applied over time.