What is the big plant with white flowers on the photo?
They both look like poison hemlock (Conium maculatum).  It can grow up to 3m tall and grows in moist areas including along creekbeds. One of it's common names is European Hemlock.  It is toxic to some domestic animals and humans.



Source: United States Department of Agriculture



Source: http://natureid.blogspot.com/2011/11/poison-hemlock-111211-elkhorn-slough.html