How do you differentiate the prepositions for bodies of water. I know seas are feminine and oceans are masculine, but what prepostions do you use?

Answer 1

Here is an "overall" look at Geographical Expressions.
The definite article is used with names of countries, continents, provinces, mountains, and bodies of water, but NOT with names of cities.

Prepositions with Place Names.

To express "to" or "in" with place names

en + feminine countries, continents, provinces
au, aux with masculine countries
dans + def. art with modified countries and continents
à with cities.

Examples: en Suisse, en Amérique, en Bourgogne

au Mexique, aux États-Unis

dans la belle France, dans l'Amérique du Sud

à Bruxelles

To express "from" with place names:

de + feminine countries, continents, provinces

de + def. art with masculine countries AND modified countries and continents

de with cities

EXAMPLES:

de Suisse, d'Amérique, de Bourgogne

du Mexique. de la belle France, de l'Amérique du Sud

de Bruxelles

NOTE: 1. with masculine countries, the definite article is always used.
2. a few cities always have a definite article in French, since the article is part of the name.
le Havre, au Havre, du Havre
la Nouvelle-Orléans, à la Nouvelle-Orléans, de la Nouvelle-Orléans

If you wish, I can give you a list of feminine countries, continents, provinces, plus a list of masculine countries but since you specifically asked about waterways, here is the list of mountains and waterways

les Alpes (f.) la Loire
le Jura le Rhin
les Pyrénées (f.) le Rhône
les Vosges (f.) la Seine
le mont Blanc la Manche
la Garonne la mer Méditerranée

Of you would like the other lists, just ask!

Sra (aka Mme)