Ford - -
I'm staying away from the design for now. Let's figure out how to fix what you have, which is where D2Cat is coming from.
By the looks of you pics, the overgrowth has caused the leaks. That was my first thought when you said overgrown.
Your tractor does have a 'hoe, so I would do what 'Cat suggested: clean it up at the surface with a 'rake, then maybe pull some back toward you with backhoe, the tractor perpendicular with the lagoon edge. I would concentrate on the stumps and heavier stuff, but not to the point where it's all ripped apart....need to be a little gentle and use some discretion so the pond isn't all torn apart...if that makes sense. I'll get to it in a bit, but there
might be block or timber sidewalls to your pond, so you don't want to tear them out.
Now - the design. A 100 years ago, I was that "County Guy" that 'Cat mentioned that went to someone's yard to help fix a sewage system. That was in New York - - so nothing I know applies, but hope I can still help.
Guessing you have no "perc," or percolation. Not uncommon where you live I bet. Your State has regulations for Oxidation Ponds. It's long, but if you search the PDF for Ponds you will find some of the specifications:
http://ldh.la.gov/assets/oph/Center-EH/sanitarian/onsitewastewater/StudyMaterialOSWWInstWk.pdf
The regs say 400 square feet of pond for up to 400 gallons/day, if the pond has straight sides with treated lumber or concrete blocks.
Your house is less than 400 gpd.
However with sloped sides and an earthen levees, although not encouraged, requires 625 sqft. of pond area. Hard to tell if yours is this design because it's obviously older. Betting it is this design though.
I didn't find the "Figures" referenced in the Code, but bet I could with some more research.
It's obvious it's not supposed to be water-tight to me, be it is supposed to retain wastewater for a sufficient period of time to allow treatment. I'm betting yours has simply "grown-in" and gotten smaller, and much more shallow than the code calls for.
But again, since I didn't see the Figures for pond design, I don't know if there's some kind of impermeable layer in it's construction.
I think the inlet/outlet piping looks about per code. The fencing is also required per code...pretty specific.
Be happy to help further if needed.