Coastal line
4. The shoreline (boundary of the water body) is determined for:
1) sea - according to the constant level of water, and in the case of periodic changes in the water level - according to the line of maximum ebb;
2) river, stream, canal, lake, flooded quarry - according to the average multi-year water level during the period when they are not covered with ice;
3) pond, reservoir - according to the normal regulated water level;
4) swamp - according to the boundary of peat deposit at zero depth
Source: "Water Code of the Russian Federation" dated 03.06.2006 No. 74-FZ (as amended on 25.06.2012)
Shoreline - boundary of a water body, which is established (determined):
for rivers, old river channels and lakes - from the average multi-year low water level during the summer period;
for internal sea waters and the territorial sea of the state - according to the constant level, and in the case of periodic changes in the water level - according to the line of maximum ebb or the line of maximum flood (determined by national legislation);
for peatlands - from their boundary corresponding to the zero depth of the peat layer
Source: "MODEL WATER CODE FOR MEMBER STATES OF THE COMMUNITY OF INDEPENDENT STATES"