Why do almost all anime series have a "going to the beach" episode? Not many anime have a dedicated episode for going to the cinema, concert, amusement park, circus, football match, camping or any other activities. But, almost all of them spare at least one of their episode for a "trip to the beach" episode. The characters sometimes travel a long distance and/or struggle among hardships for this trip.


Is is just for fan service (showing boobs and bikinis)?
Is it related to a strong cultural interest?
Or, is this because of a psychological project of the Japanese government for encouraging Japanese youth for swimming? (This reminds me of USA TV series: In almost all shows, it is a must that at least one episode must be dedicated to a gay character, one episode for a Jewish character, and all good working computers are Apple (except for the ones which get hacked or broken).)


So, what does make beach so special in anime?
Is is just for fan service (showing boobs and bikinis)?


Mostly yes. Occasionally there are plot points or setting circumstances that require a scene be on a beach (legitimate reasons that is, like a romantic beach walk with an imprtant conversation, rather than poor excuses for bikini parades)

For example, the Pretty Cure franchise has one Beach Episode per season, but, it's not for fanservice. The girls never wear swimsuits and they don't swim at all. [TvTropes]

Sometimes it is used as a 'breather episode' to let the audience take a break from the intricacies of the plot. 


  Is it related to a strong cultural interest?


Many Japanese will travel to the beach on a trip during the summer. This is common in many modern cultures. However, the Japanese have their own beach traditions too, like smashing watermelons at the beach, which is not common in the West.


  Or, is this because of a psychological project of the Japanese government for encouraging Japanese youth for swimming? (This reminds me of USA TV series: In almost all shows, it is a must that at least one episode must be dedicated to a gay character, one episode for a Jewish character, and all good working computers are Apple (except for the ones which get hacked or broken).)


I think you're over thinking this a little :P If the Japanese government wanted to encourage youth to swim - they wouldn't be targetting the otaku demographic, which are stereotypically stubborn basement dwellers who don't go outside much