Learn Hardcore German: Die Sonne scheint hell über dem Fluss.

In German, certain prepositions require specific cases. The preposition über here indicates a location (where something is happening), and it’s combined with the dative case. dem Fluss is the dative form of der Fluss.

Could I have used “über den Fluss” instead?

Yes, if there was movement across or over the river (for instance, Der Vogel fliegt über den Fluss – “The bird is flying over the river”), über would be followed by the accusative (den). In the sentence Die Sonne scheint hell über dem Fluss, there is no movement, just a location, so the dative (dem) is correct.

What does hell mean here, and can I replace it with another word?

hell means “bright” in this context and describes how the sun is shining. If you want a synonym, you could say something like klar (clear), but hell is the most common choice to describe bright sunlight.

How is scheint conjugated?

scheint is the third-person singular present tense form of the verb scheinen. The conjugation in present tense is:

ich scheine
du scheinst
er/sie/es scheint
wir scheinen
ihr scheint
sie/Sie scheinen

Is the word order here flexible?

Yes, German word order is somewhat flexible, but keeping the verb in the second position is key. You could say, for example, Hell scheint die Sonne über dem Fluss, but that would sound stylistically marked and less natural. The most standard form is Die Sonne scheint hell über dem Fluss.