I have an idea for a world where land prevails over water and what waters there are are largely relegated to scattered lakes of varying sizes. Some of these lakes would be mega lakes, the size of the Mediterranean. Maritime travel in ancient times was a lot more efficient than overland travel, and was the main artery for trade. With maritime regions being pocketed, trade would be largely regional, and the development of civilizations would be discrete and therefore divergent from one another. This is what attracts me to the setting.
But I'm wondering what the salinity of these pocket lakes would be? My understanding is that outflow to the oceans in our own world is what cleanses the various inland bodies of water of their salt content, so that their existence allows everywhere else to remain clean. In the world I'm imagining, would it be the case that some lakes would be salty and others not, depending on the contours of the landscape (how much inflow vs. outflow a given lake receives)?
Going beyond this, how would salt content be likely to influence the development of a civilization? My thoughts would be that a civilization bordering a freshwater lake would be better off due to its usefulness for irrigation and human consumption. But I also understand that salt was a valuable resource in the pre-modern age, due to its efficacy in preserving food, so that salt-water (and the option to dry it in the sun) could yield a supply of this important commodity. I like the idea of there being some 'dead' lakes, where civilization is either entirely absent or scarce due to the lake's inability to sustain human life. I'm not sure if water salinity could cause this, though.