May the Firth be with you...

Well, I've been working like a dog on WonderA's boudoir-I topped over 5 miles of Fitbit steps without leaving the house and that was mostly up and down the ladder, so at about six I went fishing on the prom, prom, prom to try and catch me a blip before supper.
For the first time this week the blips weren't jumping and I had to knuckle down and net a seascape I rather pompously call 'High tide at The Joppa steps'
It ain't great, certainly not excellent but hey, it's a blip people.
As I walked back to prepare WFT's supper I was thinking ...this Firth thing, is it a sea, an estuary, a river or a sea loch ?