Floating pennywort on UK rivers and canals: the worst case we've seen
Hydrocotyle ranunculoides can double in volume every 5–7 days in warm weather — here's why catchment-scale response is the only option.
Floating pennywort is the most aggressive aquatic invasive on the UK list. Stands that fit in a domestic pond in May fill the surface of a canal pound by August.
Identification
Bright glossy kidney-shaped leaves 3–7 cm across, floating in dense mats with white stems trailing into the water. Tiny greenish-white flowers in summer. Often confused with the native marsh pennywort, which has much smaller round leaves and is not invasive.
Control approach
- Mechanical removal by weed-boat or grab on accessible reaches.
- Hand-pull on smaller stretches, with off-site disposal under controlled-waste protocol.
- Follow-up aquatic-approved glyphosate on regrowth from fragments.
- Three-season monitoring at minimum — fragments survive winter on damp banks.
Reviewed by
The survey team
PCA-certificated surveyors, Japanese Knotweed Elimination
PA1 / PA6A certificated surveyors who carry out the site visits, write the management plans and sign off the reports issued to lenders and solicitors.
Reviews the technical, legal and lender statements in this article.
What this page can't tell you
- Guidance is general. Identification, treatment choice and timescales can only be confirmed by a site visit — photographs alone are indicative.
- Lender and insurer requirements vary by institution and change over time. We state what is typically accepted, not what any named lender will accept on your case.
- Guarantee (IBG) eligibility depends on the plan chosen, the survey findings and the underwriter's acceptance. It is not automatic.
- Legal points summarise published law and guidance current at the review date. They are not legal advice.
Last reviewed · Questions on anything stated here: 07582 869979
Think you've found knotweed? Send us a photo.
Free written identification from a PCA-certificated surveyor — no obligation.
Free identification