No further up the main path has nothing to do with the fish pool, it has everything to do with the...main path lol.
The speaker was probably referring to a person who enters the area from the road across the farm yard. So from that angle, you can enter one end of the main path.
If you keep walking from that end, the main path will reach a bridge over a fish pool.
This entire sentence can be rephrased by putting “further up the main path” in the beginning and its meaning will still stay the same.

修饰哪个都无所谓，都在一起。桥 池

我不会用crossing
会用 over
前者蛮奇怪的