Ford 3910, John Deere 420C, Kubota G32XKS, IH 2606, Bad Boy Maverick-60"
I think I'd look into it a little "deeper".
While it may work, it may also pose a hazard to some aquatic life due to leaching high alkaline compounds. Consideration for the type of water and whether it's a pond, river or lake with refresh cycles. I don't know. I'm just saying you may want to get a professional's opinion.
I would think you would go with concert pillors
and use them as pilasters so they don't sink!
Frank L. Wright used pilasters in Japans Imperial
Hotel and when the earth quake hit Wright's
building was the only one standing in 1923.