The most promising of 13 herbicides for the control of southern naiad (Najas guadalupensis (Spreng.) Magnus) were acrylaldehyde (acrolein), mono-N,N-dimethylcocoamine and di-N,N-dimethylcocoamine salts of 7-oxabicyclo[2.2.1]heptane-2,3-dicarboxylic acid (endothall), 6,7-dihydrodipyrido[1,2-a:2’,1′-c] pyrazidiinium salt (diquat), and 1,1′-dimethyl-4,4′-bypyridinium salt (paraquat). Acrolein and the 2 alkylamine salts of endothall gave the most rapid kill of southern naiad but retreatment was necessary at the end of 16 weeks. Diquat and paraquat were the 2 most promising materials evaluated. Large scale applications of acrolein, di-N,N-dimethylcocoamine salt of endothall and diquat confirmed these results. Diquat and paraquat were the only herbicides of the 13 that were not toxic to fish.