A composition and method for treating a fracturing fluid comprising produced water with high levels of dissolved solids using a polymer crosslinked with a boron compound and a high pH alkylamine buffer. The composition improves the viscosity stability of the fracturing fluid at elevated bottom-hole temperatures, particularly when the fluid has high levels of calcium and magnesium. The composition is particularly useful with polysaccharides, including galactomannan gums, such as guar gum, locust bean gum, and karaya gum, and allows for the use of the preferred boron compound crosslinkers in high total dissolved solids fracturing fluids without the pH destabilization problems encountered with the prior art.