A designated Site of Special Scientific Interest, Brechfa Common, in Powys, mid-Wales, hosts a variety of small and larger ponds and pools, the most impressive being Brechfa Pool.

Brechfa Pool is a very special site as it supports a number of restricted and rare freshwater species in Wales including Pennyroyal Mentha pulegium and Pillwort Pilularia globulifera. The wider site also hosts species such as Fairy Shrimp Chirocephalus diaphanus, Medicinal Leech Hirudo medicinalis, Mudwort Limosella aquatica, Common Toad Bufo bufo, Great Crested Newt Triturus cristatus and Violet Crystalwort Riccia huebeneriana.

Unfortunately one of the main threats to the site is the presence of the non-native invasive species Crassula helmsii. This plant out-competes other freshwater species on the site and there is a risk that if visitors are not careful, the plant may spread to other smaller ponds and pools on Brechfa Common. Interpretation will be the key to prevent spread whilst we wait on tenterhooks for a sustainable biological control for this invasive weed to be developed.