Hallo geozeisig,
 
"A swimming area is an officially designated and marked place [...]"
 
"[...] Historically, this tag has been used as the "primary" tag for a bathing place by some mappers, but this usage is discouraged [...]"
 
"[...] When not to map  
Keep in mind the Verifiability rule: You should only map a leisure=swimming_area if there is some way to verify the outlines. [...]"
 
"[...] If there is no verifiable marking that designates where swimming is allowed/suitable then no swimming area should be mapped. [...]"
 
Quelle:  
https://wiki.openstreetmap.org/wiki/Tag:leisure%3Dswimming_area
 
Brauchst du das noch deutlicher?