How come rivers don't run out of water?
How come rivers don't run out of water? Basically, in normal settings, the cycle of rain keeps rivers and lakes at normal levels but under certain circumstances like severe drought they can dry up or become very low. Rivers can dry up because of humans too. Like lower 100 miles of the Colorado River is dried up because of too much human consumption / dams.
Why are oceans salty but not lakes?
This is primarily because rivers continuously receive fresh water from rainfall and melted snow, diluting the salt content. Most lakes are also not salty for similar reasons. They receive freshwater from rivers and precipitation, which dilutes any salts. However, there are exceptions.