These reserves lie on the border between Free State and North West provinces and surround the Bloemhof Dam, an impoundment on the Vaal River. The area is generally flat, with a few low koppies and ridges, and varies in altitude from 1 228 m to 1 271 m a.s.l. It receives an average rainfall of c. 500 mm per year, which falls mostly in summer (January–March). The annual average minimum and maximum temperatures are 0 °C and 32 °C respectively.
Sandveld Nature Reserve protects a remnant patch of the eastern form of Kalahari Thornveld, which projects into the Grassland Biome. The thornveld in this region previously covered a much greater area. The central section of the reserve supports some excellent dense stands of Vachellia (formerly Acacia) erioloba savanna, with V. karroo, V. heteronuera and Brachiaria nigropedata as co-dominants. The Bloemhof Dam Nature Reserve consists mainly of grassland, which borders the dam.
Although the level of the Bloemhof Dam can fluctuate substantially, there are times when it remains low for extended periods because the Vaal Dam upstream captures the major part of the catchment waters. In such conditions, pans form and the exposed dam basin is colonised by grasses and extensive stands of annuals. When the dam is full there is virtually no exposed shoreline.
The dam regularly supports more than 5 000 waterbirds and on occasion more than 10 000 individuals. When the water level is low and islands and aquatic vegetation are exposed, the system becomes highly productive and suitable for many waterbird species. For example during April 2016, when the water level dropped to 18.8%, more than 3 000 flamingoes were counted, of which about 70% were Lesser Flamingo Phoeniconaias minor and the rest Greater Flamingo P. roseus. Several mixed heronries are at times found around the dam, supporting various breeding egrets, herons and cormorants, and occasionally more than a thousand breeding pairs. The dam also regularly holds significant numbers of Caspian Tern Sterna caspia, Great Crested Grebe Podiceps cristatus, White-breasted Cormorant Phalacrocorax lucidus, African Darter Anhinga rufa, Goliath Heron Ardea goliath, Western Cattle Egret Bubulcus ibis, African Spoonbill Platalea alba, Yellow-billed Stork Mycteria ibis, Egyptian Goose Alopochen aegyptiaca, South African Shelduck Tadorna cana, Yellow-billed Duck Anas undulata, Cape Shoveler A. smithii, Knob-billed Duck Sarkidiornis melanotos, Spur-winged Goose Plectropterus gambensis, Red-knobbed Coot Fulica cristata, Pied Avocet Recurvirostra avosetta and a few pairs of African Marsh Harrier Circus ranivorus.
The Kalahari Thornveld surrounding the dam supports several large raptors and terrestrial species, including White-backed Vulture Gyps africanus and Kori Bustard Ardeotis kori, as well as the occasional Cape Vulture G. coprotheres. The bushveld around the dam holds Red-crested Korhaan Lophotis ruficrista, Kalahari Scrub Robin Erythropygia paena, Pririt Batis Batis pririt, Barred Wren-Warbler Calamonastes fasciolatus, Marico Flycatcher Bradornis mariquensis, Crimson-breasted Shrike Laniarius atrococcineus, Sociable Weaver Philetairus socius (breeding), Scaly-feathered Finch Sporopipes squamifrons, Violet-eared Waxbill Uraeginthus granatinus, Black-faced Waxbill Estrilda erythronotos and Shaft-tailed Whydah Vidua regia.
Global threatened species are Lesser Flamingo (2 100 individuals) and Kori Bustard. Regionally threatened species are Pink-backed Pelican Pelecanus rufescens, Caspian Tern and Greater Flamingo (900 individuals). Restricted-range and biome-restricted species are Kalahari Scrub Robin, which is common; Barred Wren-Warbler and Sociable Weaver, which are fairly common; and White-bellied Sunbird Cinnyris talatala, which is uncommon. Congregatory waterbird species are Great Crested Grebe, Little Grebe Tachybaptus ruficollis, African Darter, African Spoonbill, Cape Shoveler, Pied Avocet, Goliath Heron, Western Cattle Egret, Egyptian Goose, South African Shelduck and Red-knobbed Coot.
Giant girdled lizard Cordylus giganteus occurs here.
White-backed Vulture previously bred in the reserve, but is now an occasional visitor. The reason for the decline in their numbers is not clear, although some do still breed in thornveld on surrounding farmland. Certain invasive plants have caused minor problems in the reserves. Two prickly pear Opuntia species are controlled with herbicides, the introduced moth Cactoblastus cactorum and cochineal insects. Prosopis has also invaded.
The water feeding into Bloemhof Dam may be contaminated with pollutants as it flows through the Sasol–Vereening industrial area. Cyanobacteria bloom in the dam at times. Angling is the main recreational activity in the IBA. It seems to be well controlled and is kept to designated areas. However, discarded fishing line does pose a small threat to birds.
The IBA consists of two provincial reserves surrounding Bloemhof Dam: Bloemhof Dam Nature Reserve was declared in 1975, and Sandveld Nature Reserve in 1980. The DWA manages the dam water level. Much of the land east of the IBA consists of cultivated farmland.
Colahan BD. 1992. Bird notes from Free State nature reserves:1991. Mirafra 9(2): 25–30.
Colahan BD. 1992. Bird notes from Free State nature reserves: January–June 1992. Mirafra 9(3&4): 55–60.
Colahan BD. 1993. Bird notes from Free State nature reserves: July–December 1992. Mirafra 10(2): 22–27.
Colahan BD. 1993. Bird notes from Free State nature reserves: January–June 1993. Mirafra 10(4): 74–79.
Colahan BD. 1994. Bird notes from Free State nature reserves: July–December 1993. Mirafra 11(2): 25–29.
Colahan BD. 1994. Bird notes from Free State nature reserves: January–June 1994. Mirafra 11(4): 57–64.
Kopij G, Nuttall RJ. 1996. Mixed heronries at Sandveld Nature Reserve. Mirafra 13(1): 11–17.
Nuttall RJ. 1993. Notes on birds breeding at Sandveld Nature Reserve, Orange Free State. Mirafra 10: 68–70.
Nuttall RJ. 1995. Sightings of interest: Free State region. Mirafra 12: 12–15.