The mean discharge of the Jämsänjoki river is about 13 - 14 cubic metres per second. There are great variations in flow rate. The pulp mill discharged its effluent untreated into Jämsänjoki for many decades. The slow-flowing river was polluted throughout its length, and large stretches of Lake Päijänne were spoiled. Fish deaths and disappearance of fish from the river were noted as early as the beginning of the 1900s. Even in the 1920s, large catches of smelt were still possible below the rapids in spring. In the 1930s, pollutants were thought to raise the water temperature to the extent that the river no longer froze over in winter.

The river water was tested by the City of Helsinki public health research laboratory. As the result, the Jämsä newspaper carried an official notice in 1933, urging the residents to avoid using river water in households. Nevertheless, e.g. the Jämsä dairy used river water. The situation deteriorated further when the bleaching plant was extended, and the debarking plant adopted drum debarking. Pulp production at Jämsänkoski continued to grow until the mid-1960s. At the same time, emissions into the waterway and air increased. Testing carried out in 1970 showed that the river water was totally ruined.

Water quality varied greatly depending on time of year. During high water in the spring, the water would contain only a few percent effluent, but during low discharge, the river was practically all effluent. The condition of the river was at its most critical in summer time, when the pH values were at their lowest. The discharge was low and a large part of the BHK load broke up in the river, bringing about methane fermentation. This resulted in an unpleasant smell and bubbling on the surface of the water. At its worst, the river water was very cloudy and porridge-like.

In 1969, the pulp mill commissioned its effluent evaporation and incineration plant. In addition, a water recycling system was built for the sorting and debarking plants, as well as the Pekilo factory which used the pulp waste liquor as raw material. In tests on the condition of the water in 1980 the water was still classified as unfit, but by 1992 it was satisfactory. Present water quality of the river is satisfactory under the Ministry of the Environment scale.


Solids ending up in the waste liquor were fibres, bark sludge, ash, slime and paper bulking agents. The solids made the water cloudy and sank to the river bed in large quantities, making it spongy. In 1980, the mill acquired a mechanical effluent purifier. Ten years later, a waste water purification plant was commissioned. Due to these measures, solids quantities fell from the 14 tonnes a day of the early 1960s to 4.5 tonnes in 1980.


Scientific information on the water quality of Jämsänjoki is only available starting from the 1960s. Chemical pulp production causes pollution of the waterway with compounds dissolved from timber, such as lignins, simple sugars, organic acids and alcohols. Lignins are slow to biodegrade and cause the colour of water to darken. The lignin loading caused by the mill peaked in 1965, at 123 tonnes a day. As a consequence of pulp manufacture, phosphorus from detergents, the debarking plant, ash in the sulphite waste liquor, and the chemicals used by the bleaching plant ended up in the water. The phosphorus load of Jämsänkoski mill in the 1960s averaged 56 kg a day.

Link: Järvien vedenlaatu kunnittain (Lake water quality by municipality)