I'd check out Rob Spanglers

I'd check out Rob Spanglers rivers.  They  have some parts that appear to be muddy by mixing acrylics.

Morning Deem!

I’d check out this one from Luke Towan:

It’s a resin method, but the result is great

For my money you can't beat

For my money you can't beat two part epoxy resin for modeling still water. Murky and muddy would be in you coloring. I was going for a slimy, dark bog look here... 

That Luke Towan video is

That Luke Towan video is great. I would look at Acrylic and resin "pour" products designed for art projects. They have different dyes for the resin that might create the right look.  

Acrylic paints

on a smooth surface, then several coats of gloss acrylic varnish also works.

Dyes and paints

My example above wasn't done with any sort of dyes or paint tints to the resin itself. I colored the bottom of the depression with craft acrylics and then did a pour of the resin. When it dried, I wasn't happy with the results so I actually put more ptches of acrylic paint colors  on top of the hardened epoxy and did another thin pour of the resin after the paint was dry and got the final result pictured.

Michael, you definitely

Michael, you definitely achieved a murky look, a blend of colors in the reflections—very well done!

Ooh! Very nice informative

Ooh! Very nice informative replies. 

I'm in the midst of making a muddy mound

that will protrude above the water when the tide is out.

Will get back to you all when I finish smoothing it out more with my wet fingers. Don't want to get this stuff on my keyboard.

A "Happy Accident"

With apologies to the great Bob Ross...

I discovered my "technique" of layering the painted and dried  colors with resin by accident and this is the only example of it so far. It requires more experimentation that I'm looking forward to if I get to expand my layout but I really feel like it gives me more control over the final effect than actual tinting of the resin with dyes or paint.

a spot on Mchael T's

I agree with Micheal T.  but use clear fingernail polish for very thin line of swamp water that has dear moss soaking and sticking out of the clear finish,  more trash helps in some swamp areas too.

Boudreaux,  B.C.E.

Deem, the muddy mound and

Deem, the muddy mound and textures of the bank and other scenery are spot on perfect.  It looks great right now, just wait until the colors and ground textures are added.

Did you check out Kathy Millat?

She has an episode on muddy rivers.

https://www.kathymillatt.co.uk/2015/11/19/model-muddy-rivers-using-resin/

I have achieved a turbid, but

I have achieved a turbid, but greenish look in previous years.  I sprinkled gravel and grit for a river bottom, and then poured two layers of epoxy.  The top layer had a single drop of Hauser Green and 'yellow', both Plaid craft paints from WalMart.  I also added a pinch of Plaster of Paris powder.  Once the second pour was cured, I top-coated the planar and very shiny surface with a thin layer of gel gloss medium and stippled it with the side of the applicator foam.  This left the surface looking naturally rippled, which outdoor water would almost always be.

Arizona Gary, Thanks, I'll

Arizona Gary,

Thanks, I'll check out her work.

Selector, Looks like moving

Selector,

Looks like moving water especially over the rocks.

J. Emerson, I finally got my

J. Emerson,

I finally got my supplies for making ground textures. I'm finding Celluclay does not get that smoothness I want like Hydrocal can achieve, but when the Celluclay cures, it is sandable. I think I'll stick with the premixed unsanded grout for making the mud banks.

Michael, You're giving me

Michael, 

You're giving me some ideas for ditches. Thanks for posting.

The bed is almost ready for

The bed is almost ready for murky waters.

I read that a thin coat of Envirotex or white glue makes a good seal before pouring Envirotex lite.

Hi Dee

 This is what I used for my sloughs, Woodlands Scenics Realistic Water along with their murky water tint. The last one is a work in progress. Kevin  

Nice and murky, Kevinn, Can

Nice and murky, Kevinn,

Can you get the murky tint in different colours, I'm aiming for something like this colour:

Dee

Woodland Scenics have seven different tints - 4 or 5 of which might interest you.  Including the murky already mentioned, there is silt, sage green, moss green and olive drab.

This is the sage green tint:

I'll try to get a better photo of the water for you.

Not sure

if this is any better as I see now it is a little blurry, but kind of gives you the idea of what the sage green looks like for the water and the bottom is painted with the olive drab and softened as it gets closer to the shores.

You can make it more or less opaque by the amount of colour you add - a little goes a long way.

Dave, Very nice looking water

Dave,

Very nice looking water there and I like the wet shoreline.

Dee

If you would like on my way to work I could take some pictures around the bay for inspiration for you. Kevin