According to Spiegel Online International, the European Central Bank intends to introduce a negative rate on cash deposits member banks make into their ECB accounts—a rate of -0.1%. This means that banks would be paying the ECB to deposit their money with the central bank: if a member deposited €100 million with the ECB, the latter would take a €100,000 fee.

The central bank’s motive is to stimulate more lending by those private and commercial banks, to get more money flowing in the EU’s economy. But with loan rates already at historic lows (the ECB itself is only charging 0.25% and intends to reduce that to 0.15%), it hardly seems likely that loan demand is the only impediment to lending—loan quality, borrower quality also are major factors.

Further, with loan rates so low—there’s no room, for instance, for a premium for poor credit risk—the cost to the lender of defaults goes up a lot: only those enormously low rates are there to absorb default losses.

This is a move that can only end badly for the ECB, and at best end indifferently for the banks and the EU’s overall economy. Banks look to make money, not just to let cash sit around twiddling its thumbs. If the ECB is going to charge a fee for making a deposit, look for the member banks to deposit their cash, instead, with each other.

Signs of this will include an increase in the markets for seven-day repurchase agreements, and variations on these. Repurchase agreements are mechanisms whereby banks will lend each other short-term (typically, seven days…) to cover momentary—and expected, even planned—cash flow shortfalls. Repos will make suitable substitutes for deposit accounts in the ECB.

Look, also, for increases in the markets for interest rate swaps—mechanisms whereby banks will trade future interest income streams with each other, typically with one exchanging a variable rate stream for the other’s fixed rate stream. These swaps generally are used to get (slightly) lower interest rates, or because the bank trading for the one stream finds that more useful to it than the stream it’s trading away. But these will make adequate “deposit” arrangements, also.

Look, among other places, for an increase in riskier “deposit” arrangements, too, with the member banks looking again to such instruments as credit default swaps and mortgage-backed securities. These devices aren’t much riskier, if they’re properly constructed and monitored, their negative press during the Panic of 2008 notwithstanding.

All of these, though, will make borrowing at least slightly more expensive, when (if?) borrowing picks up—hence the “at best indifferent” aspect of the ECB’s move from the private market’s perspective. On the other hand, deposits with the ECB are a major source of the funds the ECB loans out. To the extent CDS and MBS (and/or other financial instruments) do go bad, and to the extent the ECB (or its governmental masters) feels constrained to bailout, again, financial instrument market participants, it’ll be hard-pressed to do so. It won’t have the deposited funds to lend on.