Certainly is fat, it could conceivably be ready for laying. Green ponds can cause big issues, but a nice UV light will kill the algae off and the filter will strain the dead stuff out. We just spent 80 quid on a filter/fountain/UV combi thing and am VERY impressed with it, it made our pond go from a very thick pea soup type substance to nearly clear within 3 days. Unfortunately I didn't have the luck that you did and only found out I had more fish than I realised.