It isn't one of the Netherlands' major birding sites, but might be convenient for someone visiting Rotterdam who only has a couple of hours to spare. ... seen over 130 species here, but then that has taken a few years.
The best time is spring, when it has breeding Marsh Warblers, Bluethroats and Redstarts among other species. Short-toed Treecreepers and Willow Tits are resident. Marsh Harriers turn up occasionally, and can often be seen on the other side of the river.
Other species I have found here include Little Ringed Plover, Ruff, Water Rail, Spoonbill, Kingfisher, Icterine Warbler (though not recently), Goshawk and Green sandpiper.
The river here is tidal fresh water, and the chance of waders is better at low tide. Tide times are about the same as at Rotterdam.
Directions: take the Barendrecht exit from the A29. Turn right (west) and drive a few hundred metres to a roundabout. Take the exit just over half-way around, and then almost immediately turn left (heading south - Carnisseweg). Turn right at the junction just before the dyke. Follow the road for about a kilometre until you reach a little road going up over the dyke; there is a car park on the other side. The paths are easy to find. src
Dutch Urban Birding
November, 2009 (Saturday) - a city park in Leiden: "Lots of good birds in the trees, including Short-toed Treecreeper and Firecrest. Redwings were migrating and flying over, as well as hanging out in fruiting trees. Rose-ringed Parakeets flew through frequently. "
list of common birds - pic