England’s Largest Fish Pass: Functionality and Impact

England’s most extensive fish pass, a £12 million undertaking, commenced official operations last week in Nottinghamshire. This structure, known as the Colwick (Holme Sluices) fish pass, measures 200m (656ft) in length, 6m (19.7ft) in depth, and 6.5m (21.3ft) in width. The question arises regarding its operational purpose. Steve Lawrie of the Environment Agency, the organization responsible for the initiative, described the structure as “Essentially it is a motorway for fish.” He further stated, “It’s fantastic. It’s a momentous occasion where we can start to realise the ecological benefits the pass will bring.” The project, which involved over ten years of planning and two years of construction, aims to enhance fish populations and contribute to the betterment of the broader natural environment. The pass is constructed around the Holme Sluices in Colwick, which form part of a flood defense system established in the 1950s along the frequently volatile River Trent. Mr. Lawrie commented, “The sluices are the largest barrier to fish migration on the Trent. In fact, they are one of the largest river barriers in the Midlands.” Consequently, species such as Atlantic salmon and the endangered European eel have been prevented from moving upstream to access vital habitats necessary for completing their life cycles. With the new pass, all fish species will now have the capability to ascend the river and deposit their eggs in the gravel riverbeds of the Trent’s tributary rivers, including the River Dove and the River Derwent. The pass incorporates 20 distinct chambers, each progressively elevated to conform to the natural gradient of the terrain. Water traverses these chambers via narrow slots, allowing fish to swim through and pause for rest within each chamber as required. According to Mr. Lawrie, “It’s quite a complex design. It can accommodate all different types of fish and their different swimming types.” He elaborated, “Some fish, which are stronger swimmers, like the Atlantic salmon may well move through the pass in a matter of minutes.” Conversely, he noted, “Whereas others with less swimming ability, like coarse fish, may take some hours or even reside in the pools for a longer period of time.” Furthermore, the design incorporates provisions for the specific requirements of eels, ensuring this critically endangered species can also navigate upstream. Mr. Lawrie explained, “It is fitted with eel tiles. In effect, they are like bristles running the whole length of the pass.” He added, “Eels swim in a slightly different way to most other fish and it’s important we accommodate their requirements.” A two-meter-high, fully automated gate is integrated into the fish pass, continuously monitoring the flow rates of the River Trent and making adjustments to the pass to align with the broader water levels. The Environment Agency projects the “direct environmental benefits” to amount to £18.6 million. This figure encompasses the enhancement of 60km (37 miles) of river, elevating its status for fish from poor to good, alongside the creation of 60km of new spawning habitat directly upstream of the barrier. These improvements are anticipated to stimulate a rise in sporting and leisure pursuits, including angling and river tourism. To inform the public about the site and its function, interpretation boards and a dedicated viewing area have also been established.