For part 1, I reduced the number of steps by coming from both ends at once.

For part 2 I used 7 heads instead of 4. This allowed me to build layer 2 of extra pond by looking at the top of the pond directly. (~~~~~ in the top layer means digging in layer 2.)

For part 3 I used a version of the basis program.

Instead of going the full length of each line, I did each pond separately. This saved a lot of steps.

All my code .