Well, the main distinction is where they are located. Lochs can be found in Scotland and Ireland whilst lakes are found elsewhere in the world. This is because the word 'loch' comes from the Gaelic languages which were historically used in these parts of Britain.

The primary difference between a "loch" and a "lake" is geography and terminology rather than a scientific distinction. "Loch" is the Scottish Gaelic and Irish word for a body of water, and it is used almost exclusively in Scotland and parts of Ireland (where it is sometimes spelled "Lough"). While most lochs are indeed freshwater lakes, the term "loch" is also used to describe sea inlets or fjords, known as "sea lochs." For example, Loch Lomond is a freshwater lake, whereas Loch Long is a sea loch connected to the Firth of Clyde. Interestingly, there is only one "natural" body of water in Scotland officially called a "lake"—the Lake of Menteith—with all others, including the world-famous Loch Ness, retaining the traditional Scottish nomenclature. Essentially, if the same body of water were located in England or the U.S., it would be called a lake, but in the Scottish Highlands, the cultural and linguistic heritage dictates it be called a loch.