| Mouth: | River Crouch |
| Source1 Coordinates: | 51.6504°N 0.5337°W |
| Source1: | Coalhill |
Rettendon Brook is a 4.795 km (3.0 mile) tributary of the River Crouch, in South East Essex. It arises in South Hanningfield and runs east through Rettendon to South Woodam Ferrers where it discharges into the river Crouch along the tidal Fenn Creek.
The catchment area of the Rettendon Brook is 10.98 km2 (1098.07 ha).[1] The catchment extends from Warren Road South Hanningfield in the west; Rettendon Little Common in the north; Rettendon church in the south; to near Shaw's farm (A132 roundabout) in the east. The catchment is approximately 5.3 km east to west and 3.3 km north to south.
From its source at Coalhill in South Hanningfield (51°39'01.4"N 0°32'01.2"E) the Rettendon Brook flows eastwards past Marks Farm, under the A130 road, to Rawlings Farm, then south of Pound Farm, east across Rettendon parish crossing the Saffron Trail.[2] It discharges into Fenn Creek near the roundabout at start/end of the A132 road, which is the normal tidal limit of the creek (51°39'00.3"N 0°35'48.7"E).[3] Fenn Creek is 3 km (1.86 miles) long and flows south to the River Crouch of which it is a tributary. The creek marks the western extent of the urban area of the town of South Woodham Ferrers. The Creek forms part of the Fenn Washland nature reserve.
The Environment Agency assesses Rettendon Brook to have a ‘moderate’ ecological status. Its hydromorphological designation is: heavily modified.[4] A summary of monitoring results for 2022 is as follows.
| Ecological | Moderate | ||
| Biological quality elements | Bad | ||
| Physico-chemical quality elements | Moderate | ||
| Hydromorphological support elements | Supports good | ||
| Supporting elements | Good | ||
| Chemical | Does not require assessment | ||
| Priority hazardous substances | Does not require assessment | ||
| Priority substances | Does not require assessment | ||
| Other pollutants | Does not require assessment | ||