[OSM-newbies] sharing ways between areas

[Joe Richards]

I am trying to put a large national park into the map here:
Permalink to NZ map of Abel Tasman national park

with the intention of making the area green and labelled as a national park.  It's a very big area so I've split it into about three areas.

The problem is that the edges of the national park go (in some places) right up to the coastline, and so I've shared the coast as an edge.

There are several problems now:
 1. the coastline appears to have 'bled' back into the main land area, creating big pools of water in the middle of the land
 2. the national park doesn't appear green, which was the main intention in the first place.  It's genuinely sectioned-off, ie no building in this national park, and only walking tracks etc.  I think the areas around this part of the map would look better with the national parks marked off (and ideally the rivers too).

What should I be doing to fix these problems?