6x6 embark with a grand river splitting into three branches complete with two built-in waterfalls, freezes in winter for easy damming. Everything the waterworker could need. Has all the required amenities. Simply abandon and reclaim to configure the embark for yourself.

Freshwater swamp biome

-No aquifer
-Some soil/clay
-Heavily forested
-Sedimentary rock
-Iron ore deposits
-Flux stone
-Calm surroundings

Don't know if there's magma.

Enjoy!

-treskies