The latest newsletter of the Wye and Usk Foundation highlights a recent severe algal bloom on the lower Wye in recent weeks - but worryingly, now these are annual events and sometimes affect the catchment as far upstream as the Ithon confluence. Visibility in the water can drop to less than 15cm on sunny days below Monmouth.
Such blooms are caused by a combination of sunlight, low flows and elevated levels of phosphate in the water. While the Foundation is working to address the latter two factors, it is frustrated that excellent results in the Lugg catchment (a drop in phosphate levels of 31%) could be adversely affected by higher levels in the Upper Wye tributaries, the Ithon and the Lynfi. An influencing factor is thought to be the significant number of farms in the upper catchment which have diversified and added poultry enterprises to their businesses.
A slow moving river allows algae to multiply many times more before it is washed out into the estuary, and the higher up the river, the more time is available for the bloom to develop before it is flushed into the sea.
Visibility in the water can drop to less than 15cm on sunny days below Monmouth.
For more on Herefordshire's water quality visit our page on this site.