The Environment agency has a number of gauging stations with data updated online twice a day (or more often when levels rise). The three links below show rivers flowing from the western Lakes. The Calder is the quickest to rise and fall, following a similar pattern to many mountain becks. Remember weather is often very localised in the mountains and the amount of rain that falls can be very different from one valley to the next.
The charts linked to below should allow you to see if there has been significant rainfall over the last 48 hours. They could be useful if you are planning a route trying to keep your feet dry or if you are a kayaker!