Pardon my persistence but I am transferring a thread to seek more info.

Please excuse my ignorance coming from the high desert country of North Central Washington in the US. Here the trout fishing is nill from late June through August due to high water temps. When the surface temps of our lakes reach above 65 most responsible anglers wait until September.

So, to my question. Do your water temps stay less than 65 throughout the summer moths?

Thanx in advance, Flymph.

I went for a rummage in the 'internet box' following your other post.
According to the EA the highest recent mean monthly water temperatures were found in the Thames Region (11.98°C or 53.564 ºF) and Anglian Region (11.87 ºC or 53.366 ºF) and the lowest in the North East Region (9.51 ºC = 49.118 ºF) ......'coz they're well hard oop norf.

From a study in Devon; (BydrologicalSciences -Journal- des Sciences Hydrologiques,37,6,12/1992)

1977-1990 Water Temperature

Black Ball Stream - Max=22.3ºC (72.14ºF) Mean=9.2ºC (48.56ºF) Min 0.0ºC (32ºF)
River Pulham - Max=21.3ºC (70.34ºF) Mean=9.6ºC (49.28ºF) Min -0.9ºC (30.38ºF)
Iron Mill Stream - Max=20.3ºC (68.54ºF) Mean=9.6ºC (49.28ºF) Min -0.5ºC (31.1ºF)

At all the study sites, the long term mean water temperature rises above 10°C (50.0ºF) in May and returns below this value during October.

Those peak temperatures would be very rare in the UK; mostly we tend to get summers on a Tuesday afternoon in July. We tend to remember well those summers which have a sustained enough run of decent sunshine to raise the water temperature noticeably. I think most anglers in the UK would expire long before the fish if we got summers which could raise the water beyond 65ºF for more than a few days.

For what it's worth here's a graph of temperature anomalies in the central UK



As you can see there is an upward trend in where the peaks and troughs occur, so we will probably have to look at it as an issue by the time my youngster has grown up.

I know these are sea temperatures but they'll give you an idea of where we sit on the globe in terms of water temperatures generally. The Devon report predicts a rise in the July mean Maximum between 1.9ºC and 2.4ºC by 2050.

Bear in mind we don't have any central continental seasonal extremes as they do in central Europe or any of the other large land masses and our weather is very scrappy as a result, giving little chance of more than a few days of high water temperatures. We tend to get one cracking good summer each decade, and treasure the memory. (Guess who's just been on a wet holiday in Scotland and the Lake District?)