The Environment Agency said the Wye is rising as a result of heavy rainfall, with flooding of roads and farmland expected over the next couple of days.
Flooding is expected to affect low-lying land and roads along the Wye from Hay-on-Wye to Ross-on-Wye. Other locations that may be affected include Byford, Bredwardine and Hereford.
The river is expected to peak at 2.2 to 2.7 metres in Hay this afternoon, at 3.9 to 4.4 metres at Bredwardine, four to 4.5 metres in Belmont, and 3.5 to four metres at the Old Bridge overnight. It is expected to peak at 3.7 to 4.2 metres in Mordiford on Christmas morning and three to 3.5 metres in Ross on Christmas Day.
The Environment Agency said further rainfall is forecast during today and into tomorrow, with river levels expected to remain high until Tuesday, December 26.
A flood alert is also in force on the Lugg south of Leominster.
The Environment Agency said river levels continue to fall very slowly but remain high at the Lugwardine river gauge as a result of heavy rainfall. Consequently, the risk of flooding remains.
Flooding to affect low-lying land and roads adjacent to the Lugg south of Leominster from Stoke Prior to Mordiford. Other locations that may be affected include Bodenham, Lugwardine and Hampton Bishop.
River levels are expected to remain high and may rise again as a result of additional forecast rainfall over the next few days.
Avoid using low-lying footpaths near local watercourses and plan driving routes to avoid low-lying roads near rivers, which may be flooded.