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Water Quality
After a difficult winter and summer it is hard to predict water quality
Water quality in Lake Pyhäjärvi was good in summer 2011. External nutrient loading received from the inflowing Yläneenjoki and Pyhäjöki rivers was slightly higher than what it had been in the past few years. Annual phosphorus loads imported by the Yläneenjoki and Pyhäjoki rivers were 8,3 tons and 2,1 tons respectively. On average, during the years 1980-2010 the river Yläneenjoki imported 8,8 tons and the river Pyhäjoki 1,8 tons of phosphorus annually.
Lake-water phosphorus concentration (21,0 µg l-1) in 2011 was slightly higher than the average (18,0 µg l-1) for the years 1980−2010. Water visibility during the open water season was 2,15 m. The phytoplankton concentration, i.e. the amount of algae, was moderate for most of the summer and no visible surface blooms were reported during the swimming season. In August, however, the concentration of Planktothrix blue-green algae increased in deeper water layers. In early autumn and last winter, turbid waters were reported by users of the lake. Particularly in the southern parts of the lake, water was turbid and brown and the visibility was poor. The increase of blue-green algae at the end of summer caused an increase in turbidity. At the same time high quantities of nutrients and particulate matter also increased turbidity. The lake was still open when large waves caused by the Boxing Day storms brought up additional nutrients from the lake bottom which were taken up by winter algae.
Figure. Lake Pyhäjärvi water total phosphorus concentration and transparency during open water season (May-October). In 2011 the average visibility was 2,15 m and average total phosphorus concentration 20,1 µg/l.
