Trouble splitting a shoreline polygon

[JillClogston]

I have a polygon of the marine waters of the Salish Sea I am trying to split into five smaller areas. I have successfully split out the Strait of Juan de Fuca and Hood Canal, however, I am trying to split along the line I've drawn below:

I have been using the sketch line and following the polygon border and I should end up with four features, but this produces many, many more. I suspect when I draw my split line I need to mark each vertex of the original border as I am ending up with several "mini" polygons along my drawn line (if that makes senses!) If so, is there an easy way to see those vertices so I don't miss any when I'm drawing my split line? 

 Thanks for the assist!
Jill

[DanPatterson · Accepted solution]

following the polygon border probably isn't going to be good, just use a cut line straight across from one shoreline to the other.  You can reaggregate parts back together once you are done and/or modify the boundaries once the major splits are complete

[JillClogston]

Thank you Dan!

Jill