water water where?
The Dealers was filmed using G-BKMM (cr.) and that's a C180K which was on Amphibs and flown by Keith Sissons. The crew needed to clear the river with a boat first to ensure a clear path for the Thames scenes. The lake scene's where filmed on a shortish lake not far away. Great flying scenes and cool movie.
There are very few lakes in the UK compared to where I fly. They mostly look like reservoirs with the odd established sailing club. Only the odd one in Wales looked like I could drop in with the Lake Bucc.... I think you probably could explore more and more options getting permissions where necessary but the density of water there is not really worth the effort.
Irish