This map is pretty cool. It looks really nice for an alpha map.
A few things jumped out at me quickly when i was running around in single player.
You have some unpacked props here - not major.
This plank is floating - again, not really major.
However, i feel this is something quite major. The whole area below mid is much MUCH too open, it really must be split up a bit, possibly with some seperator down the middle and some more stuff happening in it on each side. Currently, you can see side to side both above and under water with there being little to no cover, this would lead to quite a few uninteresting fights.
It also may be worth having some indicator in the water to show where you cant go out any further.
Also of note is that i found it pretty unintuitive having mid be the opposite direction of where you spawn, and that water messes with explosives (you can rocket jump 3x as far) - though this map is very heavily water based so may just have to deal with that.