We understand that these reservoirs are valued spaces and an important landscape for visitors and the surrounding communities. We're working closely with the Environment Agency, Natural England and our specialist ecology contractor to carry out a wide scope of surveys and assessments.
The projects would deliver several environmental benefits including;
- The restoration of natural salmon habitat
- Removing barriers to fish and eel movement
- Restoring natural flows and sediment transportation
- Habitat enhancement such as tree planting, which form an integral part of our planning applications.
A full suite of ecological surveys have been carried out. This started with initial habitat survey and scoping, which then led to further bat, otter, reptile and invertebrate surveys to make sure that we captured all wildlife concerns and can assess potential impacts and mitigation as part of the planning application.
How will the project impact Arctic charr?
The removal of the weir should have a positive impact because a physical barrier has been removed, increasing migration opportunities for the fish community and allowing them to move more freely in, and out of Crummock Water, increasing population numbers.
An assessment of the substrate in shallow spawning activities has been carried out. Effectively, there will be a temporary reduction in the optimum spawning habitat and an increase in sub-optimal habitat for Arctic Charr. With time, the substrates (stone sizes) will naturally start to return to their previous state and provide an ideal spawning habitat.
The removal of the weir will have other more subtle changes relating to lake hydromorphology, changes in water level and silt deposition may have both positive and negative impacts on the spawning activities of Arctic Charr. Other changes relating to the wider fish community may also influence Arctic Charr communities such as restoring connectivity for other species like brown trout and salmonids.
We'll ensure that contractors appointed to carry out the work are experienced at working in sensitive locations, following practices during the construction period to protect the local landscape and habitats including sediment control to reduce impact to rivers, streams and lakes with measures in place to reuse materials in the wider scheme.
How will the project impact aquatic plants along the lakeshore?
Shoreweek Littorella uniflora, which a defining feature of the qualifying habitat of the River Derwent and Bassenthwaite Lake Special Area of Conservation (SAC), was recorded in significant abundance during the aquatic macrophyte survey around much of the Crummock lakes' shoreline, with most of the population recorded in the southern end of the lake. Surveys and assessments have concluded that a drop in Crummock Water would be expected to have only minor effects on the predominant macrophyte species in Littorelletea habitats.
Over 27 macrophyte species were recorded in Overwater and the most abundant species were widely distributed with rarer species limited to one or two discrete locations. The survey confirmed that the aquatic macrophyte community for which Overwater was designated continues to include most of the characteristic species noted in the SSSI citation. Two invasive species Crassula helmsii and Elodea nuttalli were found in abundance and strict biosecurity measures will be required.
Chapelhouse was recorded to contain 18 macrophyte species. The most abundant and widespread being the invasive species Elodea nuttalli.
Many of the macrophyte species growing in Crummock Water, Overwater and Chapelhouse are physiologically adapted to cope with seasonal, inter-annual variations in water levels.
Isoetid plants are reported to be 'stress tolerant' species and adaptable to periods of exposure caused by changing water levels. Therefore, it's hypothesised that these species within Crummock are likely to adapt once the weir is removed. However, it is possible that negative changes to the distribution of the isoetid populations might be observed as they locally compete with each other to re-colonise the new littoral zone.
So, whilst short-term, inter-annual fluctuations in water level are unlikely to impact significantly on the overall macrophyte composition, it is hard to predict with a high degree of certainty what the long-term impact of a permanent lowering of the water level at Crummock and Overwater would be. It is also not possible to say with a high degree of certainty that any observable impact would be small or insignificant. This is going to have to be monitored.
Removal of the weir and the re-naturalisation into a free flowing stream at Chapelhouse means that macrophytes characteristic of lake habitats will be lost and emergent riverine macrophytes will thrive. A National Vegetation Classification survey (NVC) of the entire lake boundary has been carried out, along with an underwater macrophyte dive survey of both Chapelhouse and Crummock.
A macrophyte dive survey is due to take place on Buttermere Dubs during summer 2023 due to the expected change in flow characteristics following completion of the proposed works.