Yellow Flowers in the river for Flower Friday

I thought these would be brandy bottle waterlilies but the lily pads are very small and the flowers do not look like the typical brandy bottle lily.   Someone will know what they are.   We swam down the river  from Windermere. It was delightful:- grasses, flowers, herons and more.  Son R swam all the way to the Swan Hotel at Newby Bridge and back- just over a  mile each way - obviously easy going down river then back against the current.  C and I turned round after half a mile and found we could walk some of the way back- extra.  Water had to be at least 25°C, it was warmer than the air at 9:00 in the morning. 
Yet another entry this week for wild flower week.  Apologies if I'm only supposed to have one. If I have to choose it will be this one