Final answer:
Ireland is the country where the Shannon River, the longest river in Ireland, forms a 70-mile estuary before reaching the Atlantic Ocean. Estuaries are important ecosystems found around the world.
Step-by-step explanation:
The country that has the Shannon as its longest river which forms a 70-mile estuary is Ireland. The Shannon River is the longest river in Ireland, and it flows into an extensive estuary before reaching the Atlantic Ocean. Estuaries, like the Shannon, are crucial ecosystems where fresh water from rivers mixes with saltwater from the sea.
For example, the Pearl River Estuary separates Hong Kong and Macau, showcasing the global significance of estuaries. Similarly, in Western Europe, there are notable estuaries such as the Exe Estuary in Great Britain, contributing to the region's diverse marine habitats.