The temperature of my pond got up to 19.4C yesterday, which is by far the highest it's been all year. For most of the summer (which has been cold and overcast), it's been hovering between 14C-16C, which hasn't been good for the creatures in it. The goldfish can't digest quickly and their immune systems are weak at that temperature, so I've lost quite a few of them to infections and some of them have an unhealthy emaciated look, though others have done fine. Also, the tadpoles develop very slowly or pause their development altogether at low temperatures, and they've developed more in the past 3 days of elevated temperatures than they've done in the past 6 weeks of cold weather.