Fishing is only allowed in the southern basin of the lake, from June 16 to March 14.
Anglers require a permit from Enable LC.
Neither the lake nor the fish in it occur naturally. The lake is rain fed, topped up from the mains when needed. Fish are introduced for the benefit of anglers and are confined to the larger, deeper, southern basin adjacent to Bellevue Field. There is a stone barrier under the bridge to stop fish moving to the smaller, shallower basin next to the railway line. However, anglers sometimes return fish there, where they breed but sometimes have difficulty surviving. They are surveyed and removed every three years. The small pond by Bolingbroke Road contains no fish.
Hot summers like the one we have experienced in 2018 highlight the challenges for both the fish and the people who manage the Common's lakes and ponds. Oxygen levels in the shallow, heated water in the lake by the railway have often become depleted (hot water carries less oxygen), causing one episode where adult fish were seen gasping for breath and another where hundreds of small fry died overnight. Gasping fish per se are not necessarily a problem - it is normal behaviour at certain times of year - but because a number of different species were displaying similar behaviour, it was put down to low oxygen levels and pumps were deployed to raise oxygen levels. Murky water is also not necessarily a bad sign, as many of the fish are bottom dwellers and stir up the mud as they eat and breed. The second incident in late July occurred immediately after the first heavy rainfall in weeks and this was not a coincidence. Although the fresh water itself would have been beneficial, it is thought that the sudden deluge brought low oxygenated water to the surface, where the small fry live, and caused their sudden death.
Enable have been considering how to improve oxygenation for some time and this year's events have made it a higher priority. The problem is that, unlike the Bolingbroke Pond, which has a pump powered by electricity from Bolingbroke Road, there is no electricity supply close to the main lake. Introducing one - even using solar power - would be expensive and disruptive and there is a valid question whether an appropriate use of scarce resources is to protect fish in an environment not best suited to them. Until such time as a solution is found, there may be further distressing incidents of fish struggling to survive.