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I did wonder if you were away on another of your picturesque missions again. It looks so interesting, the scenery is amazing ..... and I quite envy you!
Just to show that the Blue Lake really is Blue here are some pics of Valley Lake which is literally next door to Blue Lake taken on the same day.
The blue is the result of some chemical reaction (not copper sulphate). The crater and lake are relatively deep.
Valley Lake on the other hand is shallow and only takes up a section of the crater(s) it is in, the rest of the land has been turned into a recreation area (including boat ramps and BBQs) for the locals - as you can see not a tinge of blue.
I said crater(s) because they used to be two separate craters which finally exploded, merged and partially filled themselves in.
A couple more snaps of Blue Lake one showing the pumping station - as I said it is the towns water supply - you can see how steep the crater walls are.