The amount of access to Matawan Creek varies greatly by the tides. At low tide you can walk completely around the perimeter of the creek and see remains of the dock where the attacks took place. However at high tide navigation around the creek is impossible and much of the dock area is covered in water.
In the summertime it is very hard to access the creek at all due to the overgrown brush and fiddler crabs that are near the base of the creek.
The following site shows you the tides for matawan. Select Matawan from the list, and scroll down to the day you wish to view tides for.
You have the higest high tides and the lowest low tides when the moon is in full phase and new phase, also the direction of the wind and recent rains has a lot to do with water levels in the creek, as it can blow the water in or out. In perfect conditions it might be possible for the creek to be completely void of water.
Below are some pictures better illustrating the difference. The First picture is taken at low tide while the second one is taken at high tide.