Protecting the Fish

As a local community group and residents of the Esk Valley we care about the local ecology and environment ourselves. We thoroughly researched the hydro project for 4 years before deciding on the type and location for the turbine.

Working together

We work closely with the Environment Agency, the North York Moors National Park Authority and the local angling community with whom we have joint liaison meetings to air concerns and address issues as they arise.

Independent expert analysis shows that the installation of the turbine will be good for both the community and the environment. The type of turbine we have chosen is recommended by the Environment Agency for locations such as Ruswarp and it has been proven to be fish friendly by independent research carried out on salmon and trout rivers like the Esk.

Fish migration

The key element of fish migration is to ensure they readily pass unharmed both up and down stream.

There are currently two independent fish passes at Ruswarp. Both of these will be retained with one being upgraded to a “state of the art” Larinier pass which was designed by the Environment Agency.

Fish will have 3 choices to pass downstream:

  • Through the turbine itself
  • Through the upgraded Larinier pass adjacent to the turbine
  • Through the baulk pass in the centre of the weir.


  • For 6 months in winter there will be a fourth route through the kelt/smolt pass at the other end of the weir from the turbine.

Weir with Passes IdentifiedIt may seem surprising that the turbine is a possible route for fish but the turbine is an Archimedes screw which turns very slowly. So slowly that fish can safely enter at the top and be gently lowered to the bottom and swim out unharmed.

Click here to see how an Archimedes screw turbine works.

Fish will have two alternative routes to pass upstream:

  • The new Larinier pass (adjacent to the turbine)
  • The existing Baulk pass (well away from the turbine)

In addition there will be a new pass for lamprey and another new pass for eels.

Water level and flow

The turbine will be installed immediately adjacent to the upgraded fish pass. This will make the new pass more “attractive” to fish by providing an extra flow of water right at the bottom of the fish pass. This flow is termed the attraction flow.

The turbine automated control system will guarantee that the fish passes get priority for the river’s flow. As the river level falls the turbine will gradually shut down. When the water level falls to the minimum level required by the fish passes, the turbine will shut down completely. This will be monitored by the Environment Agency under the terms of the abstraction licence.

Noise limitation

There is a stringent noise limitation imposed by the planning authority because there are dwellings on the opposite river bank. To comply with this the top end of the turbine (which houses the electrical generator) will be completely covered in an acoustic enclosure and the turbine itself will be completely covered.

An independent acoustic survey shows that noise levels will be “significantly beneath the night-time ambient noise levels”.

Monitoring the fish

Before the turbine was installed our close liaison with the Environment Agency allowed them to establish a research project to monitor the migratory fish movements at Ruswarp using state of the art 3-D underwater tracking.  Salmon and sea trout were tracked in Autumn 2011 and Autumn 2012 before construction and commissioning of the turbine.  Tracking was carried out again during the Autumn migration seasons in 2013, 2014 and 2015 after commissioning.  Reports on the 2013 and 2014 results were published in 2014 and 2015 respectively and can be seen by following the links. 

The final report that included the Autumn 2015 results together with the final analysis, discussion and conclusions was published in December 2016. It too can be seen be following the link.

The executive summary from the report says:

An opportunity to improve understanding of the potential impacts of low head hydropower schemes on migratory salmonids arose on a scheme proposed for Ruswarp Weir (the tidal limit) on the River Esk in North Yorkshire. This installation, constructed in 2012, consists of a single Archimedean screw turbine co-located with a refitted fish pass. Prior to 2012 the main fish pass was a step-pool design; as part of the redevelopment of the site this was refitted as a Larinier pass following best practice guidance. The micro-scale behaviour of upstream migrating salmonids in relation to hydrodynamic and environmental cues that attract and guide fish at fish passes was investigated between 2010 and 2015 using an acoustic tracking study to identify any impact of the hydropower scheme on fish passage through the site and to obtain evidence to improve best practice guidance for co-location of turbines with fish passes. The analysis of the tracking data for sea trout post-commissioning and the comparison with the baseline identified five key results:

The proportion of tagged sea trout that successfully passed the weir (overall passage efficiency) varied markedly between years and the average overall passage efficiency post-commissioning (47%) was not significantly different from the baseline (35%). The post-commissioning study identified that 73% of the sea trout that returned to the weir after tagging successfully ascended via any route.

The proportion of tagged sea trout entering the array (attraction efficiency) was significantly higher post-commissioning (62%) than in the baseline (35%) although this too varied markedly between years. In all years of the post-commissioning dataset the vast majority of sea trout that approached the weir were attracted to the co-located Larinier pass (96%).

The fish pass efficiency of the main fish pass structure reduced significantly from 100% in the baseline to 67% post-commissioning for tagged sea trout detected in the array (although this varied from 56% in 2014 to 81% in 2013). The main fish pass changed from the step-pool pass in 2011 to the Larinier pass in 2012, prior to the commissioning of the turbine, adding a confounding factor to the baseline.

The delay between arrival in the fish pass pool and eventual passage was, whilst statistically significantly greater post-commissioning (median 2.69 [0.79 – 17.28] hours) than during the baseline (median 0.28 [0.09 – 1.41] hours), was not of energetic consequence given the overall scale and duration of the sea trout migration. It is possible that this delay may have unknown consequences for successful passage through altering motivation to migrate or predation risk.

There was some evidence of attraction of fish to the area in front of the hydropower outfall screens, which was most apparent when the turbine was active at river flows <6.28 m3 s-1, when the weir was not overtopping and the turbine abstraction was >0 m3 s-1 and <3 m3 s-1. However, this area is also the deepest part of the pool so it was difficult to determine if the sea trout were seeking refuge in deep water, being distracted from finding the fish pass plume by the outfall from the hydropower screw or utilising this area of the pool during their approach to the fish pass entrance.

The comparable overall passage efficiencies pre- and post-commissioning indicate that overall passage through the site has been maintained. However, the relatively low pass efficiency observed for the Larinier pass may be of concern and mitigation measures to improve the pass efficiency could be addressed. There is no evidence that the variability and changes in these passage metrics were related to the activity of the hydropower scheme.

Ruswarp fish migration research results published in peer reviewed international journal

The results of the research conducted by the Hull International Fisheries Institute at Ruswarp before and after the installation of the turbine have now been published in the journal Marine and Freshwater Research after presentation at the First International Symposium on Hydropower and Fish Management held in Australia.

The full text of the paper Upstream passage of adult sea trout (Salmo trutta) at a low-head weir with an Archimedean screw hydropower turbine and co-located fish pass is available via the link.

The paper incudes discussion of the implications of the findings.  They will help to determine best-practice designs and operation at other hydropower schemes on rivers with migratory salmonid fish.