Removal of the Marybank Weir in the Balnagowan River, Scotland

Introduction

The Balnagowan is a small but highly productive river in the Cromarty Firth watershed, located in the Scottish Highlands. While the principal river in the area, the Conon, is a notable Highland salmon river, it lacks the wildness of the Balnagowan. The Balnagowan is a rare example, as it remains heavily wooded on both banks along much of its course. This contributes to its productivity, providing excellent feeding grounds and habitat for fish communities throughout the lower and middle reaches. Resident brown trout are abundant, extending up to the headwater streams, and the river traditionally supported a very strong run of sea trout.

However, in recent years, it has become evident that the primary issue for fish and other species in the river is the prevalence of man-made barriers, many of which are now entirely redundant.

Project context and opportunity

Fish passes have been installed at several barriers on the river, and while salmon and sea trout do make it upriver in modest numbers, juvenile year classes are not consistently present every year. Despite the river being classified as having ‘good ecological status’ by the national environmental protection agency, the Cromarty Firth Fishery Board, which is the leading organisation in this project, has been actively working to address the ongoing anthropogenic stressors affecting the river and its wildlife.

With funding now in place, this long-term management priority has finally been realised. The removal of the Marybank Weir will open up a 14 km stretch of highly valuable habitat, restore natural river flows, and reinstate the natural processes of sediment transport, which are crucial for the river’s health and productivity.

Project aims

The primary objective of this project is to restore passage for anadromous salmonids; however, it is by no means a single-species endeavour. While the Fishery Board is committed to the conservation of fish, their remit extends much further, encompassing the stewardship of waterways and riparian zones throughout the entire watershed.

The aim is not only to achieve measurable outcomes, such as increasing juvenile densities of salmon and sea trout upstream of the weir, but also to realise wider benefits by restoring natural geomorphic and hydromorphic processes. This will, in turn, benefit native freshwater invertebrates, other fish species such as lamprey and eels, and the broader ecological communities.

Project achievements

The Marybank weir on the Balnagowan River had been a significant barrier to fish passage since its construction. While the weir was passable under higher flows, the long concrete apron and poorly designed fish pass meant that salmon and sea trout required optimal conditions to ascend. As a result, the Cromarty Firth Fishery Board applied for funding from the Open Rivers Programme and successfully secured the resources needed to remove the weir. Work began in mid-September 2024, and the weir was fully removed by October.

In the short term, this project has successfully restored natural sediment and flow regimes to the immediate area. Anecdotal evidence suggests that fish passage has been eased; a salmon was seen ascending the area within minutes of the removal of silt traps and heavy machinery!

Moving forward, the Cromarty Firth Fishery Board will continue to monitor the river channel to ensure it stabilises as naturally as possible. Early indications suggest that some excellent juvenile habitat has been uncovered, with runs and riffles now present where there was previously a slow, deep pool unsuitable for juvenile salmonids.