How do you tell the difference between a 1977 Eisenhower Silver Dollar and a Copper Nickel plated Eisenhower Dollar! i don't know if mine is made of river or not?
Highly unlikely to be silver as no silver planchet had been used by the mint since 1975 and those were in San Francisco. Since you don't mention a mintmark I assume yours is from Philadelphia. I know there were a few error 77-D halves made on leftover Bicentennial silver planchets that were sent to Denver by mistake, but I don't know if there were any silver 77-D Ikes as well.
There are some 77-D 40% Silver IKE's. As late as 1976, the US Mint was producing 40% Silver proof and business strike coins at the San Francisco Facility in addition to CnClad Proof Coins. Rejected CnClad planchets were set aside and then sent to the Denver Facility for use in the production presses. A few of the 40% planchets were mistakenly added to the CnClad rejects and included on the shipments. The same thing happened in 1974.
You can also check the weight. Clad Ike weighs 22.68 grams. Silver Ike weighs 24.59 grams. Chances are that your 77 is clad. TC
Mine is a 77 Denver Mint but the side has some Copper Color to it... so does that mean it is definitely not silver?
They struck all the 40% silver Bicentennials by the end of 1975. No it doesn't. The silver planchets that were used for the Bicentennials were 40% silver clad and COULD still show some copper color on the edge. Weight and/or specific gravity would be needed to know for sure if they are 40% silver or coppernickel clad.
Or if it's a circulated piece, you can do what all the non-collectors do and try the drop test. Drop the coin from a half inch or so off the table, a silver 40% will still have a higher pitched and distinctive ring to it. Probably the more crude way of doing it and not exactly numismatic friendly. I would try option A (edge check) and B (weigh in) before I do this.