Regent's Park boating lake?

Park and boating lake are correct but not Regent's. Quite a bit east of there. It was a mystery to me why, on a blazing hot Sunday afternoon, the boats were all moored and covered up in the middle of the lake rather than being hired out. Still, at least the gulls were enjoying them...

Victoria Park?

That's a splendid east London park and it does have a boating lake but it's not there. You need to carry on going east...

Valentine's Park?

Almost due south of there. You'd be ....... mad not to guess it now!

Then it must be Barking Park, or I am barking mad.

Barking Park it is. Hooray!