The Netherlands' Princess Maxima has joined a thousand other swimmers braving a two-kilometer tour of Amsterdam's ancient canals to raise money for charity.

Amsterdam's murky canals are not officially designated as safe for swimming, but they are flushed with fresh river water nightly. Maxima wore a wetsuit to protect her from the chilly water.

Maxima is married to Crown Prince Willem-Alexander and is the mother of his three daughters, who follow him in the direct line of succession to the throne.

The Amsterdam City Swim is performed annually for a different charity. Proceeds this year go to combat amyotrophic lateral sclerosis, the debilitating condition also known as Lou Gehrig's disease.

The princess was joined by several Dutch celebrities, including past Olympic swim champions Pieter van den Hoogenband and Marleen Veldhuis.