A survey conducted by Irish Business Against Litter (IBAL) shows that only 16% of coastal areas and waterways are clean, with the River Tolka, the River Barrow and Cork Harbour being 'heavily littered'.
The survey found that while the majority of Irish towns are clean, its beaches and waterways are not.
The business group studied 42 beaches, harbours and river areas around the country.
It revealed that only one in six were deemed 'clean', while 14% were classed as 'littered' or 'heavily littered'.
The areas were monitored by the Environmental Education Unit of An Taisce over the course of the summer.
IBAL said Cork Harbour at Midleton was "subject to dumping, with heavy levels of land-based food related items and large numbers of traffic cones and household appliances discarded in the water".
There were more than a dozen tyres dumped at Tolka River at Annesley Bridge, as well as bicycles, a shopping trolley and child's tricycle.
The group said in the River Barrow at Carlow there was "a very definite heavy litter presence … with a wide variety of regular litter, both land- and water-based".
Salthill emerged as one of the cleanest beaches, alongside Curracloe in Wexford and Seapoint in Dublin.
The report praised Salthill as a "well used and cared for environment" where a previous issue around dog fouling had been tackled.
There was "a virtual absence of litter" at Curracloe beach, while Lough Rea was commended as "an excellent site in terms of litter and overall presentation. The water was spotless".
Conor Horgan of IBAL said the survey was about protecting tourism and recreational assets, but was equally about global impact.
"The litter we encounter in these areas will typically enter our seas and add to the problem of marine litter, which is threatening our very survival," he said.
Worldwide, billions of kilos of discarded plastic can be found in swirling convergences in the oceans, making up about 40% of the world's ocean surfaces.
Recent studies have also highlighted the potential impact of marine litter on our climate, as plastic consumed by plankton may impair a key role of the ocean in trapping CO2 from our atmosphere.