Water is a key feature of the Caithness landscape, with distinctive wildlife as well as social and economic uses. Rivers and lochs are important for recreation and sport. The water quality and quantity is uniquely dependent on the management of habitats within their catchments.

All of Caithness freshwater systems are highly regarded by local people for their recreational, scenic and environmental value. These pristine waters sustain important populations of Atlantic salmon, sea trout, brown trout, sticklebacks, eels, European otters, water voles, freshwater pearl mussels and various types of birds. Pipistrelle bats can be seen at dusk feeding over bodies of open water.

Caithness is bisected by its two principal rivers, the Wick and the Thurso. Their flood plains form a fertile band of land running south-east and north-west through the county respectively. The Rivers Forss, Thurso, Berriedale and Langwell all start as peatland burns and mineral rich springs deep in the heart of Caithness. In places, these rivers have cut gullies, whose steep sides harbour rich vegetation. Pyramidal bugle and prostrate juniper are important species here. Along the river banks the estuarine sedge and holy grass are nationally rare.

Caithness lochs range from nutrient-poor peat lochans (oligotrophic) throughout the ‘Flow Country’, to nutrient-rich lochs (eutrophic) such as St Johns Loch. In between are a number of lochs with intermediate nutrient levels (mesotrophic) such as Lochs Watten and Scarmclate. The biodiversity of the lochs is highly dependent on their water chemistry, which in turn is influenced by the nature of the surrounding rocks and soils. A good number of lochs contain a calcium-rich pale mud known as marl, and these lochs are particularly rich in character.

Most Caithness lochs sustain healthy populations of fish, notably brown trout, sticklebacks and eels, while Loch Calder also has ferrox trout and Arctic charr. Some like Loch More may contain salmon at certain times of the year. Virtually all lochs have an immense diversity of insect life including an abundance of mayfly, damsel flies, caddis fly and olives. Molluscs and crustaceans such as pea mussels, snails and freshwater shrimps are abundant in the fertile lochs of Caithness. These invertebrates form an important part of the diet of trout and the local bird life. Trout in turn are eaten by otters and rarer birds like divers and osprey. Aquatic plants range from bogbean to stonewort, and many lochs contain weed beds, which provide important shelter for fish and insects.

River Thurso walkway restoration project

Pockets of open water, reedbed and fen such as at Loch Lieurary, near Westfield or Loch of Durran near Castletown can be found within hollows of the rolling farm and croft land. The mosaic of arable land, fen and damp grassland is important for lowland breeding waders such as lapwing, curlew, snipe, redshank and oystercatcher.

A diverse and colourful range of aquatic plants is found in these open water and wetland habitats. The wetlands are carpeted with an array of flowers including marsh marigold, ragged robin, northern marsh orchid and water avens. There are three nationally scarce pondweeds and one scarce water lily. Four lochs have around their margins the nationally rare narrow small reed and one loch has the only known population in the world of the Scottish small reed.

Wetlands are being managed within agri-environmental schemes