After a difficult winter and summer it is hard to predict water quality
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.
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.