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Self-healing materials are those that can recover from physical or chemical damage autonomously. To be applied in underwater applications such as water treatment, self-healing materials need to demonstrate sufficient healing ability in complex water matrices. Herein, we investigated how monovalent (NaCl) and divalent (MgSO4) ions at concentrations relevant to brackish and seawater salinity impact the self- healing efficiency of a model 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS) and N,N′-methylenebis(acrylamide) (MBA) hydrogel. It has been assumed that divalent ions would form ionic bonds and act as crosslinkers between viable functional groups (negatively charged oxygens, etc.). However, our results suggest that this assumption needs to be reconsidered. Under concentrations relevant to seawater (35 g/L), magnesium ions hindered self-healing efficiency by ∼30% as measured by recovery of ultimate tensile (UT) strength. On the other hand, they improved self-healing efficiency by ∼100% as measured by recovery ofUT strain. A similar trend was also observed for sodium ions. The chemical crosslinker ratio when doubled did not impact self-healing efficiency. These results challenge the assumption that divalent