Weeds That Thrive in Autumn: What to Look Out For in Your Waterways

As the seasons change and temperatures begin to drop, aquatic weeds don’t simply disappear. In fact, several species thrive during the cooler, wetter months of autumn, taking advantage of reduced competition and steady nutrient levels in the water. Left unchecked, these weeds can spread rapidly, impacting biodiversity and disrupting the balance of your pond, lake, or watercourse.

Common Aquatic Weeds in Autumn

1. Duckweed
Duckweed is one of the fastest-spreading aquatic weeds and can remain active well into autumn. Its tiny floating leaves form dense mats that block out light, starving other aquatic plants and reducing oxygen levels for fish.

2. Canadian Pondweed
This submerged plant remains persistent throughout autumn, especially in still or slow-moving water. It grows in thick clumps, which can tangle with equipment, restrict navigation, and reduce the open water available for wildlife.

3. Blanket Weed (Filamentous Algae)
Blanket weed thrives where there are high nutrient levels, and autumn leaf fall can provide the perfect fuel for growth. It forms stringy, dense masses that can clog water features, reduce oxygen levels, and create an unsightly surface layer.

Why Autumn Weed Management Matters

Many landowners assume weed control is only needed in spring and summer, but tackling problem species in autumn can make next year’s growth much more manageable. Regular maintenance also helps protect biodiversity by ensuring your water remains healthy and balanced throughout the year.

Tackling problem species in autumn can:

Prevent spring explosions – stopping weeds from overwintering in large numbers.

Protect biodiversity – keeping waterways open for fish, invertebrates, and waterfowl.

Maintain water quality – reducing the build-up of decaying plant matter that lowers oxygen.

At The Aqua Contractor, we use mechanical methods to manage aquatic weeds in a safe, environmentally friendly way. By cutting and removing excess growth, we help restore your water to a healthier state, ready for the season ahead.

If you’ve noticed weed build-up in your pond or lake this autumn, now is the time to act.