This engineer technical letter describes criteria for predicting blast effects from detonations in water and instrumentation techniques for monitoring such effects. The purpose of this ETL is to assist USACE Commands in the intelligent use of underwater blast monitoring to prevent damage or injury to nearby structures, equipment, or aquatic life from water shock effects. Rock blasting in lake or river bottoms will produce a combination of ground and water shock effects. Some items that are of concern during underwater blasting are: gates, structures, boats, fish, fish eggs, etc. Damage or injury thresholds for these items are difficult to quantify or are not readily available. These damage thresholds must be set or assumed by the user.