18/05/2026
Brook Lampreys (Lampetra planeri) spawning at a site in the Lower River Shannon Special Area of Conservation (SAC). This species is a Qualifying Interest of this Natura 2000 site and is the smallest of the three Irish lamprey species.
Lampreys are primitive vertebrates belonging to an ancient lineage dating back over 350 million years. These “living fossils” are a vital part of the biodiversity and ecology of healthy rivers, often making up a large proportion of the total biomass in smaller watercourses.
Lampreys play an important role in nutrient cycling in rivers. They have also been described as “ecosystem engineers”, as they create and maintain suitable habitats for a range of other aquatic organisms through their burrowing and spawning activities. They are a key component at the base of the freshwater food chain and provide a food source for many other species of conservation importance.
Lampreys use very specific microhabitats in rivers and are considered indicators of good hydromorphological status. The larvae (ammocoetes) live in fine silt deposits in slow-flowing areas, while adults require clean gravels in riffles for spawning. They also rely on overhanging trees for shade and protection from predators.
Because their larvae are filter feeders, lampreys are also indicators of good water quality. They live buried in river sediments for years, where they are exposed to whatever contaminants accumulate there. Substances such as heavy metals, persistent organic chemicals, and microplastics can be ingested as they feed. Their foraging and sediment-burrowing behaviour increases their exposure to these pollutants, especially compared to more mobile fish such as salmonids.
River maintenance and other instream works pose significant threats to these habitats. Activities such as dredging can remove or disturb larvae, while clearance of riparian vegetation eliminates critical cover. Physical alterations to rivers, and even small weirs, can fragment habitat and block local migrations.
Brook Lampreys remain hidden in riverbeds for much of their lives, only surfacing briefly in spring to spawn and die. Yet they serve as a “canary in the coal mine” for our rivers, quietly signalling the health, or decline, of these fragile ecosystems.
Monitoring lamprey populations can help us understand the impacts of pollution, habitat degradation, and climate change on our rivers. Healthy rivers support clean water, biodiversity, recreation, and fisheries. All of these benefits depend on the natural processes and habitats that species such as lampreys rely on.
