As part of the construction of Osney Lock Hydro, a new fish pass was installed, allowing fish to move freely up-river for the first time in two hundred years.
The use of an Archimedean screw turbine for the hydro is a positive choice in terms of allowing sediment and fish to move downstream, but it cannot provide upstream passage for fish, so an upstream fish pass was also built to help fish ascend what would otherwise be an abrupt rise of up to 1.8m.
The pass is around 27m long and 1.6m wide, and is fitted with 500mm polypropylene brushes to create a cascade of pools which slow down water and help fish to move up the slope.
Migratory species need to be able to access habitats which are only or mainly available in higher parts of the river system, e.g. for spawning or other life stages. Other species that have historically not been considered migratory are also now understood to benefit if they can move freely within the river system, in terms of population resilience, for example.
At Osney, as well as the potential for salmon and trout arriving via the Thames, many other species are present which may benefit from increased mobility. The decline in populations of some important species (eels, salmon) has led to particular concern to redress the balance by regulating to ensure that, wherever possible, access to suitable habitats is maintained – or is created – even if they have not been accessible for many decades due to the presence of weirs and sluices. One aspect of this regulation is the opportunity to require fish passage to be added or enhanced where a new development such as a hydro scheme is undertaken.
Godstow to Osney stretch of the Thames: silver bream, common bream, dace, tench, pike, roach, bleak, chub, perch, carp and barbel with a good range of sizes/age classes especially for the roach perch, chub, pike and bleak.
The Osney Stream: chub, roach, dace, perch, pike, gudgeon, bleak, silver and common bream, barbel, ruffe sizes ranging from fry to numerous large chub.Bullheads and lamprey eels are also to be found.
Source: Environment Agency Fisheries 2011