Traditional New Year's dive is basically thousands of people getting a swim in a freezingly cold water anywhere around them. Since these things tend to get commercialized, the chilling plunge is an organized activity managed by a big soup brand.
If you are lucky, you can taste hot chocolate or Dutch pea soup afterwards. It is a lot of fun! On average, 10,000 people take a swim this day on the beach of Scheveningen! If you want some place less crowded go for another location out of 60 possible around the Netherlands.