Another way to access the mouth of the cap is to park behind park royal and walk the trails in (I think its quicker than ambelside too)..
If you come along the highway and exit at taylor way, go straight south on taylor and it will cross marine drive into Park Royal. Follow that street south and leads behind the mall. There is a stop sign and then the road hooks right...while the river looks great there, thats native land, go another 100 yards or so. as you drive along that road, there is a gravel shoulder where people park (on your left) and the trail head is almost directly across from the ramp that leads to park royal's roof top parking.
Park close to the trail head and walk in to below the rail way bridge. If you are new to the area, below the railway bridge you need a salt water liscence and above that bridge you need a fresh water liscence. Keep in mind that between the rail way bridge and the marine drive bridge, thats native land so as I noted above, its best to avoid that area.