One rough guide to the ion content of a body of water is to measure the water's electrical conductivity, or conductance. The conductance of a body of water is a function of the quantity of ions contained in it, the equivalent conductance of each ion, and water temperature. In the case of Lake Biwa, conductance is high in its tributaries but low in the lake water, enabling the degree of mixture of the river water and lake water to be measured. The diagram shows the conductance at Akanoi Bay in Lake Biwa, illustrating how the high-conductance river water loses its conductance and becomes diluted as it enters the lake.

Rough guide to ion ingredients of water
The conductance of a body of water is a function of the quantity of ions contained in it, the equivalent conductance of each ion, and water temperature.

Lake Biwa
Conductance in tributaries is high.
Conductance of the lake water is low.
This method indicates the degree of mixture of river water and lake water at the river mouth.

When the high-conductance river water enters the lake, the river water loses conductance and becomes diluted.