Try messing with the [RIVER_MINS:300:280], how many puny fish-happy streams are around.
Less streams and lower drainage might give lakes. Hopefully evil lakes with zombie swans and pelicans.
Trying medium region... put bias on low drainage. From 70 rivers to 12 rivers: no luck.
From 70 rivers to 90 rivers: two lakes. With elven names.
180 rivers: two puny lakes and one frozen lake-like glacier next to main glacier. And.. looks like a freshwater sea far south.
Increasing low-drainage mesh thingy. From 8-6-1-1-1 to 1000-6-1-1-1. Got TEN tiny lakes where the mountains surround a valley.
North edge, a huge light-blue (probably freshwater) sea.
Roll world again: got 8 lakes. Thick river bumps into north edge, makes lake. I see. The edges of the world are tall cliffs.
Roll world again: zero lakes, 3 seas.
Roll world again: zero lakes, one huge sea.
Roll world again: zero lakes, one huge sea.
Roll world again: four lakes nestled by mountains, two seas.
Increase mountain peak count: change from 5 to 20. Seven lakes, zero seas.
Eight lakes, two seas. Seven lakes, three seas. Zero lakes, huge sea.
Zero lakes, two small seas, one huge low desert. Six lakes, one big half-frozen sea.
So, cold areas and scorching areas hurt your sea and lake formation. One might want a everywhere-temperate world with even rainfall for lakes.
(changes rainfall variance to 55 and temperatures to 45-65.) 3 lakes, 1 huge sea.
(78 variance, 50-65) no lakes, giant central desert, neat. Roll: 2 lakes, 5 seas. Roll: 0 lakes 2 seas.
(change to 70 mountain peaks) 2 seas, central mountains. 1 sea and 1 desert ex-sea. Sweet evil forest in the big desert.
(temperatures to 40-55) 3 small seas, 1 ex-sea.
(several changes) Whoa, the world has a central very evil mountain range. 3 seas. Gotta go view that very-wide rivermouth.
(embark with 8x8 area to see wide river) 24-wide river at z-level -7. -2 Level's river drops in a grand waterfall to the -7 river! Impressive. And had a cavern collapse at start. 72 fps and everybody idles except the carp. This place is too peaceful. (normally 320+ fps at 3x3 embark)