Lough Funshinagh, Protected lake in County Roscommon, Ireland.

Lough Funshinagh is a lake set on limestone bedrock spanning around 430 hectares in County Roscommon. The water level shifts noticeably with the seasons and rainfall patterns.

Lough Funshinagh was proposed as a Site of Community Importance in November 1997 and designated a Natura 2000 site in May 2019 under the Habitats Directive. Statutory Instrument No. 211 of 2019 established it as a Special Area of Conservation (site code 000611), protecting turloughs and rivers with muddy banks.

The name Loch Fuinseann means 'lake of the ash tree' in Irish. Since 2016 a blocked swallow hole has kept water in the basin, and Bewick's swans, whooper swans and curlews have declined around it. In March 2022 a 2.5-mile pipeline to the River Shannon was begun to drain the lake, then halted by an injunction obtained by Friends of the Irish Environment; nearby houses are now ringed with sandbags.

The area is accessible year-round, though spring and summer provide the best conditions for observing wildlife. Visitors should be prepared for changing weather and varying water levels that may affect how you move around the site.

The lake bed holds swallow holes sealed by a clay layer; when that seal breaks, water can drain in as little as two days. In 1996 the lake emptied almost completely after 19 August, stranding large numbers of fish.