king willem-alexander of the netherlands is celebrating his 48th birthday .
took part in a water-borne procession along a canal in dordrecht .
was joined by his glamorous wife , queen maxima , and their daughters .
the 43-year-old queen was resplendent in a cheerful raspberry get-up .
king 's day - or koningsdag - is a national holiday in the netherlands .
celebrations include ` king 's parties ' and eating lots of tompouce pastries .