Hi Chris, due to the green element I think Coniston has a speed limit of 10mph now and all the lakes are about the same. I will check if there is anywhere you can jet ski and get back to you.
The Gondola on Coniston is a nice relaxing trip if you fancy it.
There are plenty of small craft for hire at Bowness and Windemere.
Will post up later in the day, having enough of driving my boat at the moment.