The Glaven catchment contains several lakes and ponds. There are around 9 sizeable lakes (over 1 hectare) situated adjacent to the river, most of which date to the late 18th and early 19th centuries when they were dug for ornamental purposes (in the grounds of country estates), or as mill ponds. Bayfield Hall Lake and Selbrigg Pond are good examples.
Smaller ponds also abound in the catchment with marl pits being common. Other pond origins include horse-watering pits, duck decoy ponds and ponds dug more recently for angling and conservation purposes.
Glaven lakes contain a range of fish species, common species being Roach, Rudd, Perch, Pike and Eel. Some of the smaller ponds also contain fishes and just a few of these have populations of Crucian Carp, a recently established Biodiversity Action Plan (BAP) species in the county of Norfolk.
Glaven valley ponds provide a hot area for Great Crested Newt, but there are also good populations of Common Toad, Common Frog and Smooth Newt. The Palmate Newt, which is very rare in Norfolk, also occurs in the Glaven valley.
Most of the Glaven lakes are high quality ecosystems with clear waters and abundant beds of submerged aquatic plants. Stoneworts (Characeae), a group of plants of conservation concern, occur in some of the lakes with at least six recorded species; Chara vulgaris, Chara globularis, Chara contraria, Chara hispida, Tolypella glonerata and Nitella flexilis occur in Glaven lakes and ponds.
As a consequence the Holt to Melton Constable region (largely the Glaven catchment) has been designated as an Important Stonewort Area by the UK plant charity Plantlife.
Other common plant species that occur in Glaven lakes and ponds include:
- Curled Pondweed (Potamogeton crispus)
- Fennel-leaved Pondweed (Potamogeton pectinatus)
- Least Pondweed (Potamogeton pusillus)
- Broad-leaved Pondweed (Potamogeton natans)
- Horned Pondweed (Zannichellia palustris)
- Pond Water-crowfoot (Ranunculus aquatilis)
- Rigid Hornwort (Ceratophyllum demersum)
- Soft Hornwort (Ceratophyllum submersum)
- Ivy-leaved Duckweed (Lemna trisulca)
- Common Duckweed (Lemna minor)
- Marestail (Hippurus vulgaris)
- Amphibious Bistort (Persicaria amphibia)
In particular Soft Hornwort is rare in the British Isles and North Norfolk, including the Glaven catchment, seems to be a key area for this plant.