I wonder if the water south of the oil lake is ocean, u could drop down other city there and built forts to reach the oil lake and that way u can get the work boat up there and after it done building a oil well, u raze there city if u don't want it.
And about the three fishes in ice land town, try building fort at there end of penisula and send a work boat through it, and if it succeeds, well enjoy.