Yellow flowers on tall wild plant

[MarcP2]

Yesterday, I found this solitary yellow plant growing down by the creek. It wasn't there last year. Today, I found a whole patch of them which also weren't there last year. In the third picture, it is mixed with brambles and other plants. Poison ivy made me keep my distance.

[MarcP2]

I guess I was wrong. I saw this plant somewhere last year, because I already have a post from last august showing it. However, I didn't get an answer in this particular plant.

[GEOSAN]

Yellow Loosestrife me thinks.

[MarcP2]

Yellow Loosestrife me thinks.

I think you may be right. I would have never thought of loosestrife. Thank you.