The harbours serving Irvine at Seagatefoot and Fullarton in North Ayrshire have had a long and complex history. Irvine's harbour was one of the most important ports in Scotland in the 16th century. Across from the main harbour at Fullarton on the River Irvine there was also terminal for the ICI-Nobel Explosives plant on the River Garnock. Much of the harbour went into decline in the 19th century when Glasgow, Greenock and Port Glasgow achieved higher prominence as sea ports. There was still some commercial sea traffic linked to local needs, though the harbour went into further terminal decline in the 20th century. The weir on the River Irvine forms the formal upper limit of the harbour.