WATER QUALITY of the Cromarty Firth
The inshore and deep channel waters of the Cromarty Firth are normally monitored on a 3-year rolling programme. Water samples are taken for chemical analysis and biological samples are taken of the littoral and benthic fauna for examination.
In 1992, the Board co-operated with the Marine Laboratory, Aberdeen, in a national survey of nutrient pollution in estuaries. This showed the Cromarty, Dornoch And Inverness firths as being the cleanest of the estuaries on the east coast of Scotland with the lowest nutrient levels. They were the only estuaries on the east coast where the nitrogen in the inflowing freshwater was lower than in the sea water. This is a reflection of the low nitrogen input (from agriculture and sewage) to the main rivers. However, nitrate levels were high in Udale Bay and Nigg Bay as usual due to run-off from agricultural land. Faecal coliform levels all passed the mandatory standard of the Bathing Water Directive.
There are many settlements on the Cromarty Firth, especially along the route of the former A9. Historically, as a settlement developed and drainage became necessary this was simply piped to the nearest watercourse or the sea and discharged untreated. As the settlements grew the impact of many of these discharges became greater especially where these were near small rivers.
As the impact on small rivers and other inland waterways was normally more noticeable with such discharges, some form of sewage treatment was provided for those ones first, leaving those with apparently less impact to the last. As a result, many of the towns and villages around the Cromarty Firth, which discharged to it, have little or no treatment.