This group is certainly one of the most popular and one where a miniHide can really pay dividends. It includes many iconic species like the kingfisher and great-crested grebes. Open water means there is literally nowhere for the wildlife watcher to hide. Exposure to wind and rain can also really affect your comfort! It is no surprise then that many nature reserves site there main hides on the waters edge. The Island Mere hide at Minsmere is a typical example.
As so often is the case, your selection of a suitable lens is really guided by the subject to camera distance. With open water this could be considerable and even the longest, most expensive, lens would not really achieve acceptable results. Heat haze and general visibility issues can also greatly affect acceptable distances. If your interest is primarily photography then managers may want to restrict these distances when creating new habitats.