Earlier studies on the relationship between mercury concentration in fish – or alternatively bioavailability of mercury in aquatic systems – and different abiotic oceanographic factors such as water temperature, pH and salinity, have shown that such associations often exist. The results are not always consistent between studies, however. The aim of this study is to investi­gate if this type of relationships can be established in Baltic herring, Clupea harengus, with the use of temporal monitoring data from the northern Bothnian Bay (northern Sweden), compiled within Swedish monitoring programmes. The abiotic factors being assessed in this study are water temperature, salinity, dissolved oxygen, pH and measurements of nutrient content in the water; phosphate, total phosphorus and total nitrogen. Relationships between these parameters and mercury concentration in herring were investi­gated using multiple linear regression. Generally however, relationships were absent, and only one significant association was found, a positive relationship between total phosphorus in water and herring mercury load. Difficulty to reveal relationships in the presence of confoun­ding factors, which cannot be controlled for when using monitoring data from the field, is suggested as one reason for the absence of such relationships. Furthermore, the somewhat incomplete monitoring data of abiotic factors likely made it hard to detect any relationships.