This mod will remain up for those which only want more swamps and sugar in their games, however, a more advanced version with desert fertility bonuses, lush river tiles, river gold, small fish lakes alongside rivers etc. has been integrated into the new major mod DLC "Salts And Soaps".

You are encouraged to try that mod instead.

Ah, I see. I was specifically thinking of turning some river-adjacent deserts into grassland.

It turns 70% of river forests and 30% of river grasslands into swamps. Said grasslands are "floodplains".

We can not add our own terrain yet. Basically the game already has a +food system for farms near rivers anyway.

Since you mention "swamps and floodplains", are floodplains just swamps next to rivers, or something more?