In this chapter, the physics of ice cover in lakes and rivers is presented. Lake ice questions are largely local due to the limited size of the basins. River ice differs from lake ice due to river hydraulics which produces large volumes of frazil ice and drives ice jams in ice decay period. Most lakes have fresh water, salinity less than 0.5‰ (per mille); it can be a significant factor in the melting period but otherwise it has a negligible influence on winter processes and ice properties. Saline lakes can be studied with the methods introduced for sea ice in the Sea Ice chapter. Here, the first section introduces freezing lakes and rivers, followed by ice formation and structure and properties of ice. Sections 7.3 and 7.4 present thermodynamics and mechanics of lake ice, and the last section focuses on river ice questions.