data - World map with clear difference between land, sea and inland waterways

I'm looking for a free high resolution map that clearly indicates the land and sea in the world. I need it to calculate distances over sea between ports. Additionally it should also include inland waterways and canals.

Does anybody know whether this data is freely available?

Answer

After some trial and error the most practical solution turned out to be:

Use a shape file of all world countries, add the Suez and Panama canal manually using software like QGIS, add the ice of the arctic and Antarctica using shapefiles as well. This gives you a map of all the places a ship can go.

I left out the inland waterways in the end. However these could be included using the link provided by Aaron.