Measurements by STUK found close to 600 micrograms of uranium per litre in the mid-depth and bottom waters of the nearby Salminen pond. Surface waters were found to contain less than 1 microgram per litre. The upper limit for drinking water is 100 micrograms.
Tarja Ikäheimonen of STUK believes that the waters of the pond will have to be neutralised or prevented from flowing onwards.
"At this point, these are personal thoughts about how to proceed. In any case the water, as it is now, must be prevented from flowing on further. This will take a few more days of consideration," Ikäheimonen told Yle.
The Talvivaara Mining Company has started an investigation into the matter.
The first phase of a leak from one of the mine's gypsum holding ponds in November spilled around 20,000 litres of unprocessed waste water into the surrounding area.