Buying in environment areas

The pool probably can’t be below ground, their concern would be any discharge from the pool (back flush) due to proximity to creek. Building height would be due to visual amenity.
The rest are all just because it’s close to the creek, the boundaries they put on those in their mapping systems are usually fairly conservative. The block probably has a building envelope and you can’t clear outside of that, that’s what my property is like. Just consider the block maintenance side of things if it has firebreaks etc..