If you build a small gap with landfill on water then biters cannot walk over the gap but the players can.
This makes it extremely easy to handle biters by exploiting this on maps with a lot of water. You simply build a safe-zone on water with the gap and no biters will reach you and you can then run in and out to easily handle biters on any difficulty level. Although this might not sound so bad and you might say it is up to each and every one to exploit this or not. But when it comes to playing these kind of levels in multiplayer it leaves out a very fun play style when this exists (since players tend to want to use the most easy way). If we were forced to take the decision to open up the path to a new iland instead then the difficulty becomes much closer to the intended difficulty of the game. It then allows you to build up a good defense at the place you plan to open up and then there would be no way to reverse this again (since you cannot "build" water).
I see three options that would improve this:
1. Make it impossible for players to walk over water gaps or...
2. Make biters able to walk over water gaps as well as the player or...
3. Make small biters unable to cross but larger biters able to cross.
