The Big Black River Basin (see figure) covers an area of about 3,400 square miles. The headwaters of the Big Black River are in Webster County in north-central Mississippi. From there the river flows southwesterly and discharges into the Mississippi River. The basin is about 160 miles long and 20 to 25 miles wide. It has no major tributaries, and many of the small tributaries in the upper part of the basin flow only part of the year. Elevations in the Big Black River Basin range from almost 50 to about 650 feet (14 to 198 meters) above sea level. The area is sparsely populated and is hilly to gently rolling terrain, with significant amounts of cattle ranching and farming (principally soybeans and cotton). Oil and gas production is a major industry in the area. About 56 percent of the basin is forested, and about 39 percent is agricultural land.
The flow of the Big Black River near Bovina averages about 28,500 gallons per second. However, in the past flow has been as low as about 500 gallons per second and as high as about 690,000 gallons per second. Use of surface water in the Big Black River Basin is relatively small. About 1.1 million gallons per day are used for irrigation, and about 1.5 million gallons per day are used for livestock.
Generally, the Big Black River and most of its tributaries are very turbid most of the time, especially in the northern part of the basin. The rivers carry large amounts of suspended sediment derived mainly from agricultural runoff. Whereas many of the streams in the basin are muddy and slow-flowing, others have relatively clear water and are swift with sandy bottoms. Overall, the water quality in the basin is generally rated as fair.