Fish Habitat
A stream or river often has a combination of shallower rocky places (riffles) and deeper pools. Pools and riffles are natural formations particularly noticeable in gravel bed rivers such as the Swale, and can add significantly to the ecological interest of a river and are important fish habitats. Pools are favourite places for trout to lurk as the water flows a little slower as it passes through. This also means organic debris will settle out providing food for insects which in turn are eaten by the fish. Pools and riffles are rarely consistent in form being re-profiled during flood events as gravels move downstream. The river constantly reworks this material and needs a supply of material from further upstream to maintain them.

Trout Stocks
Trout stocks in the main river exhibit temporal and spatial variability. Data extracted by the Environment Agency from 1976 survey data, indicates that recruitment is very limited in the main river, with almost all trout fry production occurring in the tributaries. Production in the tributaries also shows the same degree of variability, most likely attributed to poor habitat and water quality.

Marrick and Dunholme Bridge
Two sites on the River Swale between Marrick and Downholme Bridge were electric fished to obtain baseline data on fish stocks during September 1999. Low numbers of brown trout were recorded which displayed moderate growth. Most recruitment was by immigration of one or two year old trout from the tributaries. At both sites there were considerable stocks of Bullheads, indicative of good water quality, but also elevated numbers of Stone Loach, suggestive of enrichment. The sites surveyed will be subjected to localised habitat improvements following the baseline surveys. Further surveys are taking place annually to assess the impact of local and area management on fish numbers.

Initial surveys indicate reduction in enrichment, and habitat improvements could increase the value of the Swale to Brown trout and other minor species, essential to the food chain.

Gill Beck and Oxque Gill
Surveys on Gill Beck and Oxque Gill have shown more work is required on Gill beck to determine the cause of reduced stocks, whilst Oxque Gill was identified as a good nursery stream. Work is to be done to improve the habitats of Clapgate Gill also a potentially good nursery stream.

Low Whita
Another survey undertaken on the main river at Low Whita, surveyed during August 2000, showed that trout numbers were up at this site as a result of good recruitment in 1997, supporting catches of 3+ fish. 2+ fish were also relatively numerous. Again the point to stress is that recruitment at this site is supported by successful spawning elsewhere - most likely local tributaries and not in the main river.