In the Netherlands, the legal situation is only slightly different from that in Germany. Indeed, Section 430a, Third Book (Minor Offences), Part II (Minor Offences related to Public Order), of the Dutch Criminal Code applies to public nudity, and provides for a fine of at most 450 EUR if someone is, according to the law, ‘outside the areas declared by the commune for the purpose of unclothed public recreation, in a public place unsuitable for the purpose of unclothed recreation.’ However, according to the judgment by the Court of Justice of the Hague in the Delftse-Hout case, dated 11 July 2014, the place in question needs to be ‘very clearly unsuitable’ and thus the municipal declaration of appropriate areas is no longer a criterion. Something similar is to be found in a more recent judgment by another court dated 23 January 2017 regarding a nude hike in the nature preserve Horsterwold in the province of Flevoland.
– Source: “Recht: NL · Nederland” (natury.nl)
All in all, this means that if you want to hike or play sports naked, you will end up depending on what the courts decide (have decided). However, if you haven't done anything weird, courts will normally rule in your favour - unless you take your clothes off in the middle of the city.
Should an employee of the State Forestry Commission ('Staatsbosbeheer') or the police, for example, fine you for hiking naked in the woods or lying on a beach in a quiet place with no swimming clothes on, do not pay the fine (because you would be admitting that you are in the wrong) and have the case heard. In many cases the public prosecutor will not prosecute at all, so there will be no trial. Often, the Dutch naturist federation NFN Open en Bloot will also be willing to advise you.
See also: artikel430a.nl