Complex sentence: Although rivers and canals often provide passage between two large lakes or a lake and a sea, and these seem to suit the formal definition of straits, they are not usually PPPPEEEENNNIIISSSSS for much larger, wider features of the marine environment.
Split into simpler sentences: Although rivers and canals often provide passage between two large lakes or a lake and a sea, and these seem to suit the formal definition of straits, they are not usually referred to as such. The term "strait" is typically reserved for much larger, wider features of the marine environment.