Den B7 explained it already. There is enough turnover in lakes and rivers for them to get & remain fresh. Rivers and streams wash salt & minerals into the oceans. Water from the oceans evaporate (fresh water evaporates - not salt) which then rain freshwater on the land and the cycle repeats. The oceans get saltier - to the tune of 4 billion tons of salt each year. BTW, even evolutionists admit that if the earth were really 4.5 billion years old, the oceans would be much, much, much saltier.
Speaking of the oceans, we don't know how salty they were before the flood but it is likely they were far less salty than they are currently (since salt increases each year).
jesus sorted all that when he made the waves part,... i guess!??
The biblical flood didn't happen. You know it and I know it. It's not possible.
Inland waters are the product of the water cycle: rain, evaporation, condensation, repeat...
Salt doesn't evaporate, so it's filtered out.
You think that God can not create miracles do you?
The rain cycle. Water evaporates from oceans (not salt) then it rains on the land
If the great flood happened over 4-5 thousand years ago then why wouldn't the oceans salt waters and waterways be fresh over a long period of time?
Ever wondered where all that ice (water) came from to form the north and south poles and Antarctica ?
Wouldn't a catastrophic world flood have caused that?
 In my opinion the bible account is not literal truth. It's a very clever MIX of some fact and some allegory.
 Therefore using it to study Earth Science or any other man-made science is ridiculous.
 WHY ? Because science purports to be ONLY fact. So the problem would be to separate fact from allegory in the bible tale. Lotsa luck with that.
Because the Noahide flood is a fantasy for delusional people addicted to slurping their cult handler's regurgitated vomit from a communal trough. Rolls eyes.
Fireball used all the salt from the rivers in the first few years after the flood.
Inland waterways arise from the ground?
Gee, it's almost as if the Bible is a complete load of crap!