Unfortunately, that doesn't include swimming at certain Iowa beaches and lakes. The Iowa Department of Natural Resources has updated its list of unsafe lakes, and the total is at a season high. Iowa DNR Updates Unsafe Beach ListThe Des Moines Register reports that the Iowa DNR has updated its list of unsafe beaches in the state, and the number has risen to 16. DNR Collects Samples WeeklyThe Register reports that DNR staff collect water samples weekly at 41 state-owned swimming beaches. Tests are conducted Memorial Day weekend through Labor Day weekend.