Currently the opencast mining is performed in North-East Estonia nearby the main water resources of the region: the Narva River and the Narva Reservoir.
In addition, the water from the Mustajogi River and also water from the Narva Reservoir is used as cooling water in the Eesti Power Plant so that all the water from the Mustajogi River flows through Eesti PP .
However, clear dissimilarity between the studied metal concentrations in different layers of sediments were seen for sampling sites 11 and 15 (the Narva River and the Narva Reservoir, respectively), showing that content of heavy metals in the upper layer is higher than in the bottom layer for sample 11 and vice versa for the sample 15.
There has been no regular hydrobiological monitoring up to now, except in the Narva Reservoir where it has been carried out since 2001.
Since 1956 the river has been dammed by the Narva Reservoir, which extends up to 38 km upstream (total surface area 200 [km.
The impact of the Narva Reservoir on riverine phytoplankton was rather weak because of the rapid turnover in the reservoir, 3435 times a year (Mistsuk & Jaani, 2000).