It's fine to go on a trip and plan a swim along the way. I don't mean swimming and lying on the beach all day before snacking. I mean …, swimming, lying down or having a picnic and continuing the trip further.
I offer some tips below, where such type of swimming is possible in Czech Switzerland, can be found in Lužické Hory or Labské pískovce.
Water reservoir Vlčí can be found above the city Šluknov. For example, you will go on a trip to Karlova údolí on the red road
Possible entrance next to the dam, very clean water
Lipová Quarry you will find during a trip from the village Lipová to Anenský vrch on the green. A beautiful clean quarry appears in the middle of the trip.
Large fir pond is on the bike path 3015 from the village of Rybniště to Jedlova.
Pleasant entrance from the side of the dam. Clean water even in summer.
Klopot lake it is hidden on the border with Germany ( left bank of the river Elbe, 200 meters up a steep hill from the shore). You can either take the Elbe cycle path or take the green path from Dolní Žleb. Input (rather a jump) from the dam, crystal clear water, cold even in summer
Naděje water reservoir waiting for you on the cycle path from Mount Luž in the direction of Cvikov or on foot from Horní Světlá along the green path.
Entrance above the dam. Very clean and cold water.