Woose
I kept a boat at Wareham for years, before even Decca Navigators were available for small boats let alone GPS.
The channels are clearly marked now.
Once you get near to the river, the channel is marked with stakes, keep closer to the middle of the channel than to the stakes, they are at the top of the bank and don't be tempted to cut corners. I've pulled many boats off the mud because they took a straight line from stake to stake.
Take a look at Google Earth, it shows the mouth of the river at low tide.