Walking access to the estuary is off Holben Parade (map here). You can park in the car park, and there is also a small picnic shelter for public use. There are two directions you can go to view the estuary from here.
Alternatively, if you want to see the river mouth end of the estuary, head past the Foxton Beach Motor Camp along Pinewood Road (take care to stay out of the way of vehicles). After around 5-10 minutes you will come out near the bollards.
Turning right from there will take you to the river mouth and ocean beach (about 15 minutes walk). You can then continue north along the beach to the Surf Club and loop back to Holben Parade. This will take you around 1 hour for the full trip.
The estuary walkway provides beautiful views, and there are signs along the way providing information about some of the birds you might see.
This scenic walkway that goes upriver along the edge of the estuary.
The path will take you past a viewing platform, where you can get good views of birds feeding and/or resting. The path and platform are wheelchair friendly.
The walkway continues up to the Manawatu Boating Club where you might see people fishing off the wharf, and boats coming and going.