A joint-lubricating composition for treating degenerative joint disorders is provided, having microalgal polysaccharides in an aqueous solution, wherein the polysaccharides are stable and non-immunogenic. Further provided is a method for treating a joint disorder by injecting into the joint a viscous aqueous solution of a polysaccharide, wherein the disorder is, for example, arthritis, and the polysaccharide originates, for example, from a red alga.
