The River Deel near Crossmolina in County Mayo, Ireland, is a 45-kilometre river that rises in the Nephin Beg mountains and flows through moorland and pastures before passing through the town of Crossmolina and entering the northern end of Lough Conn. It drains a catchment of approximately 63 square kilometres and is the largest tributary of the River Moy system. The river's character shifts considerably along its length, with more remote and lively conditions in the upper reaches and calmer water in the lower stretches approaching Lough Conn.

Kayaking on the Deel has grown in popularity in recent years, with paddlers exploring the river both upstream from Crossmolina and in the lower reaches near Lough Conn. The river has been used as a venue for river safety and rescue training courses, suggesting it offers suitable conditions for skills development when water levels are adequate. Paddlers and local clubs have noted that higher water levels following heavy rainfall produce the best conditions for a river run, indicating the Deel is level-dependent and most suitable after significant precipitation.

The lower reaches near the shore of Lough Conn pass by historically significant ruins, including Castle Gore and Deel Castle, both dating to the 16th century. The last structure on the site was built in 1790, damaged during the 1798 rebellion, and ultimately burned during the Civil War in 1922.

The river supports notable biodiversity, including rare white-clawed crayfish and freshwater pearl mussels, both of which are sensitive indicator species. The presence of these species reflects the river's ecological importance, though water quality concerns have been identified in certain sub-catchments, particularly related to phosphorus and ammonia runoff from peat bogs and forestry on peat. Paddlers should be aware that the river flows through working agricultural and peat landscape, which influences water quality in places.

The river also supports salmon and trout fishing, which is a significant activity along its length. Paddlers sharing the water with anglers should be mindful of this, particularly during fishing seasons.