The Khibiny tundra - is the land of lakes. The lakes were formed due to low water permeability of the crystalline rocks, mass of tectonic depressions and fractures but primarily due to large amount of precipitation. Naturally, lakes are closed areas which accumulate or take all the inflows, for example, of both surface and underground waters. Moreover, lakes can control the river flows, chemical and biological reactions can happen there.
The largest lake of the region is Imandra, its water surface area is equal to eight hundred seventy six square meters. The deepest lake is Umbozero, its depth can reach one hundred fifteen meters. Both lakes can be referred to the largest lakes in the European part of Russia.
The lakes are mainly open or running-water lakes. Rivers that take off the open lakes are: Niva from Imandra, Umba from Umbozero. Originally, the lakes are divided into two groups - glacial and tectonic lakes. The majority of lakes represent small glacial water entities of circular shape with water surface area less than one kilometer and a depth of three-six meters. Large and medium- size water entities are of tectonic origin.
During winter and in windless weather during summer the flow rate in the lakes is significantly less than that of the rivers. But at the same time under the influence of wind the flow rate of the water surface layer is strongly increasing.
Freezeup in the lakes is long enough - about two hundred twenty days per year. The ice cover thickness is about one meter, in harsh winter it can increase up to one meter and a half. However, in river heads, intense ground water discharge sites, in narrow bays and in warm waste water inlet areas the ice cover is becoming relatively thin or alternates to open water. The latter can be seen, for example, in Imandra lake in the narrow Yokostrovsky bay under the bridge and in Molochny bay near the canal where warm water comes from the Kolskaya NPP. The open water in lakes is more dangerous for travelers than in rivers because they are deep, surrounded by thin ice and often powdered with snow. That is why when travelling in winter through lakes or rivers these places are better to find before and keep away. In summer it is also dangerous to be found in the lake water far away from the coast as low temperature of the water can easily result in overcooling.
Lake water as well as river water is quite fresh and clean. In the areas under anthropogenic impact the water is contaminated, it contains admixtures, non-ferrous metals and other contaminants. Lake water is similar to river water by its chemical composition.
Lakes and rivers are the sources of water supply for the towns, settlements and enterprises of the region. The deep ones are used as water - collecting areas and hydro power stations. It is water-collecting areas that provide for commercial use of water resources. In spring they collect melt water. In summer and, especially, in winter due to accumulated water reserves the hydro power stations can produce more energy.
Usually dam is built where river valley narrows or in the river head in lake to set a water storage. Several hydro power station chains are built in the river to get more benefit from the power of the water flow. Dams provide for water level and flow energy increase along with preventing fish sprawning run. For that matter, special fishways are built but unfortunately they are inefficient.