Freshwater INNS: what’s the problem?

Freshwater invasive non-native species (INNS) damage rivers, canals and lakes causing significant ecological, economic and recreational impacts.

Invasive mussel species attach readily to pipes causing blockages and damage to infrastructure, consequently costing water companies thousands to manage.

Invasive plants out-compete native plant species and dominate whole waterbodies. As a result, they cause environmental damage and impact our enjoyment with the environment.

How do INNS spread in the environment?

INNS are accidentally moved from one site to another attached to clothing or equipment used in the environment. Unintentional movement of INNS leads to the spread and establishment of new populations.

Biosecurity measures are used to prevent the spread of INNS. Cleaning equipment used in one location before moving it to another will remove any INNS present and prevent their spread to new locations.

What did we test?

We tested the effectiveness of hot water sprays in killing freshwater INNS in the field. We investigated two invasive animals and two invasive plants that are a threat in the UK.

Killer shrimp

Zebra Mussel

Floating pennywort


To mimic large pieces of equipment, such as vehicles and boats, we attached species samples to a metal backboard.

Pressurised hot water spray applied in field conditions

Species attached to board

How hot is hot?

Firstly, we measured the maximum temperature of the water as it contacted our samples when spraying from different distances and machine-set temperatures.

When spray was applied for 15 seconds, relatively low on-contact temperatures were achieved even when spraying from a short distance (Table 1).

Table 1. On-contact average water temperature of hot water spray treatments


Percentage mortality after 24 hours following hot water spray.

Killer shrimp

Zebra Mussel

Floating pennywort


Is hot water spray effective?

  • High-pressure hot water spray applied from 10cm for 15 seconds killed all of the killer shrimp and zebra mussel (Table 2).
  • When sprayed from longer distances or shorter durations, we found high but not complete mortality.
  • In contrast, hot water spray was ineffective in causing mortality in crassula, even at 90 seconds of exposure.
  • Fragmentation and complete mortality was seen in floating pennywort following both hot and cold spray treatments, therefore the pressure of the spray caused this mortality.

Stephanie Bradbeer

PhD Student, Faculty of Biological Sciences, University of Leeds

Based at the University of Leeds and working with the Environment Agency and South West Water, Stephanie Bradbeer's research focuses on invasive species management and biosecurity. Her work assesses the effectiveness of biosecurity methods, including hot water sprays and examines biosecurity behaviour and awareness of stakeholders.

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