Hi there. Long time lurker, newly registered, and in need of some assistance.
Okay, so my fort is in its eighth, prosperous year, and my dwarves grow wealthy from turning the pleasant rolling hills and the lush green forests into smoldering ashes, barren rocks and large piles of gold and silver treasures, later to be locked for all eternity in a sealed underground vault.
Since I hate ambushes, I decided to seal off most of the overground map with stone wall (dirt trenches being a solution more fitting to goblin engineers), and using the nearby river as a natural moat, controlled by a single bridge. After over two years of construction, the wall is finally ready. Only one section remains: the one immediately adjoining the river. Being way upstream, this particular spot has been a fertile breeding ground for various fish. My masons, being a bunch of sissy civilians, were scared of fish and refused to complete the wall.
Instead of casting the sorry lot to the Dungeons of Despair to do battle with wild cougars and rabid raccoons for the rest of their miserable lives, I decided to send in my elite marksdwarf to clear the river with his bolts. I stationed her a few squares away from the bank, ordered her to fire at animals and stay close to the station. Since carps were nowhere to be seen, I figured it would be a safe and quick bloodbath.
She started sniping, killing a few of those scaly bastards, before running out of ammo and into the river for some extreme dwarf-on-fish wrestling action. She drowned shortly thereafter while still smashing fish skulls with her crossbow. Her loyal war dog quickly followed her to a watery, fish infested grave, and a stupid peasant decided to join in before I remembered to forbid the corpse and the loot.
Now I'm pissed off. I got two dwarves, one of which was valuable to the fortress defense and a loving mother of four, rotting at the bottom of the river, the water of which run red with the blood of crippled fish. The killer Pike, Ilreal, swims joyously in the middle of the stream, mocking the land-creatures with its bloodied fins.
The Killer Pike cannot be suffered to exist. I began planning a punitive expedition to purge the upstream portion of the river river from all life with as much needless brutality and flying fish chunks as possible. I filled a room to 2/7 with water, and sent my five axe-wielding champions to patrol it until they can swim better than the damn river fish themselves. I will have my brutal dwarven vengeance.
Problem is, I don't have much experience with making amphibious dwarves. What sort of skill level should I aim at before sending them to the river? Will they be able to get out on their own once the job is done, or should I make sure they have an escape channel and a staircase handy? Will they be swept downstream? Will they die the moment they're grabbed by a fish? Can this plan even work, or should I choose the safer (and more cowardly) option of training additional marksdwarves and declaring Pike hunting season?