The south loop is completely overgrown. To get through would require a machete and hedge clippers (plus leather gloves and long pants and shirts). Definitely not a hike for kids. 
Could be reinvigorated with a work party. But this hike (as featured in the Andrew Weber & Bryce Stevens book "60 Hikes Within 60 Miles: Seattle, 3rd ed, 2016) no longer exists as such.

Every time I do this hike I'm impressed by its beauty; and impressed by how neglected and overgrown it is. Lots of blackberry, nettle and other weeds. There are viewing platforms and signage that are inaccessible because it's so overgrown. I was unable to get all the way around the south end, turning back when I could no longer tell if there was a trail. Would someone please organize a work party or bring a machete?

The positives: lots of great views of the Cascades, Baker, Rainier, the river and the winding channels; a large variety of birds and lots of them; a unique environment.

Quick walk around the Spencer Island and Langus Riverfront trails Sunday morning in the sunshine.  Parking at Langus is free and plentiful, (the other little lot under the freeway was nearly full already.)  Our route was generally along Langus, east and over the Spencer Island bridge to the abandoned dredge barge but skipping the overgrown SE section, then back around the southern trails along the Snohomish river.  Total mileage ended up just under 5 miles and basically completely flat.  Full restrooms at Langus were open and in good condition, the sanican on the eastern side near the dredge barge was open and functional.  The main trails are in decent condition, but the SE loop continues to be completely overgrown.  The paved sections are quite nice and flat, fully power/wheel chair accessible.  

Lots of wildlife out, bald eagles, heron, ducks, sparrows, swallows, etc.  We had something hiss at us from some bushes next to the trail, never saw it but sounded like an annoyed Opossum maybe.  Beautiful views north to Mt Baker, east to the cascades and south down the valley.  For all you marine craft nerds - I stumbled on some additional info about the abandoned dredge barge on the eastern side of Spencer Island.  Turns out it is a WWII era Yard Seaplane Derrick, YSD-61, originally operated at Naval Station Whidbey at Oak Harbor then sold by the Navy in 1961 to Western Marine Construction Company who  used it for 50 additional years.  Another working example can be seen locally is the YSD-67, now the MV Puget, and operated by the Army Corp of Engineers at the Hiram Chittenden Locks.  Neat, eh?  For more info do a Youtube search for “YSD-61”.   A relatively easy and accessible walk with beautiful views and a bunch to see.  

Link to further information about the coming updates and revitalization project for the area - https://wdfw.wa.gov/species-habitats/habitat-recovery/puget-sound/estuary-restoration-projects/spencer-island-restoration-project

Lovely day for birding at Spencer island, the loop was narrow and overgrown at parts but decent to walk along. We saw some interesting birds (my birder friends would have more specifics, but the binoculars were out often). We took the last parking spot at around 12 but there’s another log close by that had plenty of openings. Not many people around, it felt like we had the place to ourselves on the most part.

Good little hike close to town! lots of bird watchers out and about. Nice loop around a marsh/wetlands with a bit of brush but mostly open trail.