vegetation is protected for a given distance from a stream centreline
From a land management point of view, this is not a desirable boundary.
I'm looking at exactly that situation myself, where some parcels I'm dealing with have pointed intrusions into them that mess up land management. Where did those pointed intrusions come from that stick into what otherwise would be a nice, regular parcel?
They are buffers around seasonal small streams, not even visible today except as slight ravines in the forest, that many years ago got recorded into the cadastral system and thereafter took a bite out of parcels that later on were surveyed. Here are two examples:
The field example is particularly annoying, in that it (in theory) prevents the farmer from plowing straight furrows right across a slight depression that is barely noticeable in the field:
But... how to deal with that depends on how much effect the law has, and whether you have to follow the law or are free to do something different.
If the law says "vegetation is protected in a region up to 40 meters from a stream centerline" that is going to create sharp angles in some cases where stream centerlines are bendy.
Consider the following image:
That shows a 40 meter buffer (in preview color) built on the stream centerline (black). If the law says "40 meters" you end up with acute angles in the change of direction of the buffer boundary.
But, if the law gives you some slack, in Release 8 you can convert the boundary area to a line, and then use the Spline transform toolbar command to smooth out acute angles.