Is it too cold to swim in the Emerald Pool in the beginning of Oct.?

Agree with Grant, the average high in October is 66 and average low is 39. I wouldn't count on it being warm enough to smiw in that cold water.

Possibly depending on your tolerance for cold. The water is always a bit cold but the hot summer makes it bearable. In Oct the weather can change day to day. It will be in the 90s one day and the 70s the next. It should also be noted that the upper pools are closed currently due to a flood. Check with the website or the rangers if they are open by then.