Everybody will swim in the rivers the same day, at the same hour, in all the European rivers, from the sources and the glaciers to the oceans.
If swimming or jumping in your river is not possible, then just organize an other event and celebrate the river !
There are many ways to get citizens involved

http://www.rivernet.org/bigjump/

...an inspiring project that captures the essence of current EU
waterprotection legislation into one single public act: at one date, at one time, people will jump into rivers all over Europe. More
(European Water Management News, 22 June 2005)

With over 250 000 visitors, the Big Jump 2005 was a success. Along 31 rivers in 22 countries, 216 official actions, 240 inofficial spontaneous jumps have been well organized !

Meet at Cumberland Basin !