I would recommend the Nikon 10-24mm f/3.5-4.5G ED AF-S.
- Very versatile focal length range
- Significantly fast aperture for a UWA
- Designed for your D5100 DX format
- High quality optics with ED glass, great sharpness, etc.
- Reasonable cost for the high grade of the lens
- Newer design and all of the current technologies such as SWM
If you are going to be using the lens around the water, I would recommend picking up a circular polarizing filter. It can help you to cut through the glare in the water and potentially see fish better with the camera. It also has other benefits in bringing out blue skies for example. Some considerations have to be made when you are using a CPL filter with UWA lenses, such as the change in blue across the sky though.