A Boat a Lake and a Picnic.
Find a lovely place were you can hire a row boat, or peddle boat. Tell you partner you have surprise for them. Put blindfold on them and lead them down to the lake. Where there is the boat waiting with lovely picnic hamper on board. Now if you can hire one for an evening remember the candles to add to the romantic ambience. You can add music with portable speakers and your Ipod or MP3 player.
Our city has river flowing through it where you can hire a Gondola with the Gondoleer. This is very romantic date you can order champagne and canapés when you hire your Gondola.
Add your own ideas in the comments section for a water themed date.