Henry I, the 3rd norman King of England, died after eating a surfeit of lampreys after going on a hunting trip while ill. Apparently eating them was against the advice of his physician. Lampreys were pretty common fare in Early Medieval Britain but are pretty gross eel-like fish that still happily inhabit English rivers today. It is likely that they weren't properly cooked, and may have been contaminated with water from the river they were fished from. England rivers were littered with weirs and eel traps, and there were several Doomes demanding Weir clearance around the country in the 10th and 11th centuries (Law of Aethelred II) as they blocked the flow of the river, but rivers remained pretty clogged anyway and likely didn't dilute/run off the sewage and waste all that well!
John I 'Lackland' probably died of dysentery brought on by eating rotten peaches and drinking wine during a military campaign.
Edward IV died after catching a chill after a fishing trip. Some have hypothesized that he died of a stroke.
All of this information is on Wiki. Use this as a starting point to find better sources. I would wager, Henry I best matches your question.