Newbie - managed to fix colour balance before but seem to have forgotten how!

[rich2005]

As I understand it, it is lack of red in underwater photos.

The attached script maybe as a starter. Unzip put in C:\Users\"yourname"\AppData\Roaming\GIMP\2.10\scripts Adds a menu Script-Fu -> Enhance -> Diving Red Filter
Then a little adjust using the Colors -> Hue-Chroma Reduce the hue value to give a little blue.

Got me to this.