Restoration works of the Salaca river

Restoration of streams is essential to improve spawning grounds

In August, the LIFE IS SALACA project started restoration work on the streams. In 2024, work is planned on three sections of the Salaca river, totalling more than 6 hectares. The works will restore suitable habitats for salmonids by removing surface vegetation and its root systems.

The Salaca is one of the main salmon rivers in the Baltic States and is also one of the most important watercourses for the conservation of fish fauna in Latvia. Unfortunately, many of the Salaca’s headwater streams are densely overgrown with surface vegetation as a result of eutrophication. The fast-flowing sections are usually the shallowest parts of the river, so the problems caused by eutrophication – increased overgrowth of aquatic plants – are most often observed in the fast-flowing sections. In the Salaca, too, in large parts of the fast-flowing stretches, overgrowth is already so intense that the substrate and current velocity of the fast-flowing stretches have been partially lost. The increased vegetation in most of the Salaca’s fast-flowing streams is made up of lake sediments. These plants are characterised by a dense root system that can form a turf up to 30 cm thick in the river bottom, thus covering the areas of the rapids and destroying the gravelly-pebbly habitats suitable for salmonid spawning. As streams become heavily overgrown with aquatic plants, the community of fish species in the river changes over time: the number of fish typical of fast and oxygen-rich rivers (salmon, sea lamprey) decreases, while the number of ecologically tolerant fish species (pike, whitefish, roach, perch) increases. Therefore, to ensure that the Salaca can continue to boast the title of the main salmon river of the Baltic States, stream restoration measures will be implemented within the LIFE IS SALACA project. At the same time, the restoration of the streams will also benefit the overall ecological status of the river, and in the long term provide more favourable living conditions for the aquatic invertebrate species that inhabit the streams, such as the river lamprey, river mayfly, thick pearl mussel, river toothless tooth and other species.

The works will be carried out using specialised equipment

The bed of the Salaca will be cleaned using a chain excavator equipped with a special bucket to remove lake-sedge and other helophytes (surface plants) that form dense growth, as well as the thick ‘turf’ formed by their root systems. The excavator is equipped with a special bucket with a mesh size of 20 x 20 cm. It is designed to leave as much of the substrate (pebbles, stones and gravel) characteristic of fast-flowing streams as possible in the river bed. In areas where the watercourses are not significantly overgrown with halophytes, the bed will be scoured using a special scouring bucket. It is important that the chain excavator is equipped with biodegradable oils, thus ensuring that no pollutants that could harm the river inhabitants will enter the Salaca during the cleaning operations.

The restoration measures will be carried out with responsibility for nature and its values

In order to ensure that the restoration of the Salaca’s watercourses is as environmentally friendly as possible and does not harm the river itself, its inhabitants or the habitats and species in the riparian area, a number of different conditions will be observed during the works:

• The relief of the Salaca channel and the profile of the shoreline will not be altered (no distinct landforms, islands, peninsulas at the shoreline, etc. altering the relief of the river bed).
  If large stones are removed from the river during the clearance works, they will be placed back in the river bed.
• The main focus will be on reducing dense overwater vegetation. The loosening of submerged parts of streams overgrown with emergent plants will only be carried out if the roots of these plants have formed a ‘turf’ which may impede the spawning of salmonids and lampreys.
• The mass of aquatic plants, their root systems and sediments removed from the river will not be placed on the banks of the Salaca or on islands in terrestrial habitats of EU importance. Prior to the works, the boundaries of the habitats of EU importance were marked on the banks.
• To minimise the return of removed plant material to the river, wherever possible, the mass of aquatic plants, their root systems and sediment removed from the river will be placed above the flood zone. In areas where this is not feasible due to topography, the removed mass will be placed in a narrow strip along the river bank without forming large mounds. In stretches where islands occur in the Salaca, it is permissible to place the removed mass on them. Different situations will be coordinated with the freshwater habitat expert during the work.
• Where possible, the substrate removed from the bed will be revised in order to return the fish, lamprey larvae and mussels removed with the sediment mass to the river.
  In order to minimise potential impacts on migratory, spawning and juvenile development of migratory fish, the works are to be carried out during a limited period from 15 July to 15 September.
• To minimise water quality degradation during the works, biodegradable oils will be used for machinery as planned, and the works will be carried out with a special bucket that minimises the removal of fast-flowing bed substrates, juvenile fish, lamprey larvae and benthic organisms from the river.

Cooperation between experts and practitioners throughout the project

The restoration of the streams in the Salaca will be carried out in close cooperation with LIFE IS SALACA experts on freshwater, fish and invertebrates, thus ensuring that the experts’ recommendations will be followed during the implementation of the works and that the best solutions will be sought in case any unforeseen difficulties arise during the implementation of the works. This will be an excellent opportunity for both parties – experts and practitioners – to learn from each other and exchange knowledge and advice so that the management work can be carried out in the best possible and most environmentally friendly way. The experience gained will also be useful for similar work in other watercourses!