The public are being advised to take care on the waters of Lough Ree and the River Shannon.
It comes as Lough Ree RNLI rescued 133 people from 42 separate incidents in the last 6 months.
Tom Maguire from the Lough Ree RNLI hopes that new markers installed by Waterways Ireland will help to reduce the number of incidents.
"The vast majority of incidents have been boats running aground on the hexagonal shoal. These are hexagonal formations of rocks just under the water between Hodson bay on the Roscommon side and Coosan point and Killinure on the Westmeath side. The good news is Waterways Ireland have installed new markers alongside the existing ones and we would hope this will reduce the number of incidents of boats running aground".