Fish Friendly Hydropower

Being UK pioneers of the Archimedean Screw turbine, MannPower has worked hand-in-hand with the Environment Agency to establish the eco-credentials of the technology. And in fact these credentials are unrivalled in hydropower generation. Unlike other turbines the unique design and relatively slow revolution speed of the turbine allows fish to travel safely along its length.

This is demonstrated in the video below, which shows some of the fish testing carried out by MannPower in conjunction with the Environment Agency and their agents, Fishtek.

Conventional turbines operate with a fast blade rotation, causing a high risk of injury to fish – as do the water pressure changes they create. What’s more the need for fine fish screening increases installation and running costs – meaning they are less cost-effective than the Archimedean Screw turbine.

Fish Studies Summary


Since 2004, MannPower has been supplying the Archimedean Screw as the fish-friendly answer to hydro generation. Although widely in use throughout continental Europe for some time now, the screw was a newcomer to British rivers, and as such inevitably raised concerns – particularly within the Environment Agency – about the potential environmental and fisheries impact of the proposed installations.


On the basis of previous studies carried out in Europe which supported the claims to fish-friendliness, the Environment Agency permitted the first UK Screw installation (on the River Dart at Ashburton in Devon) to run unscreened for a year whilst monitoring was taking place. During that time, marine biologist Pete Kibel of Fishtek Ltd – in consultation with the Environment Agency and members of the Fish Pass Panel – has undertaken comprehensive live fish trials at the site and the results are extremely positive.

Phase 1

Safe passage for salmonids and brown trout

Phase 2

Safe passage for eels and kelts (also demonstrating that fish would not be harmed or unduly delayed by attempting to ascend the screw)

Phase 3

Safe passage for all species of course fish (also demonstrating that these fish do not actively choose a bywash as an alternative route)

Literally thousands of fish passages have been monitored and recorded using underwater cameras at the intake, inside the chamber of the Screw itself and at the outflow to assess the effect of the Screw on salmonids (including smolts and kelts), brown trout and eels. The trials looked at fish passage across a broad spectrum of sizes and turbine speeds, possibly the most impressive of which was the safe passage of a kelt measuring 98cm in length and weighing 7.6kg.

The studies conclude that the Archimedean Screw turbine is indeed fish-friendly with no adverse physical effect on fully grown fish or kelts; at most 1.4% of smolts sustaining limited and recoverable scale loss (NB ‘at most’ because these were wild fish and quite likely to have sustained some scale damage prior to entry into the turbine) and just 1 out of 160 eels (0.64%) suffered minor and recoverable pinching to the tail. In addition, behavioural and migrational patterns across the species have been shown to be entirely unaffected by the turbine.

The implication of these findings is extremely positive for the economics of micro-hydro in the UK. Sites previously written off for hydro development owing to fish protection issues can be revisited, and the cost of installation for an Archimedean Screw turbine will be significantly reduced by the requirement for only minimal screening.