Idaho Mitigation Plans: How a Junior Ground Water Right Keeps Pumping

The choice an Idaho junior water right holder actually faces

When a senior water right holder makes a delivery call and the Director of the Department of Water Resources finds material injury, the juniors causing the shortfall face two outcomes. One is curtailment: the well stops. The other is mitigation: the well keeps running, and the junior delivers water or other compensation that makes the senior whole.

The mitigation docket is the longer of the two. IDWR lists 19 delivery calls. It lists 48 mitigation plan matters, and they carry 1,458 filings between them, the earliest dated April 2007 and the most recent July 2026.

The rule that governs all of it is one page long.

What Idaho's Rule 43 requires

Mitigation plans are governed by Rule 43 of IDAPA 37.03.11, the conjunctive management rules adopted under Section 42-603, Idaho Code.

Submission. A proposed plan goes to the Director in writing and must contain the name and address of whoever submits it, the water rights it is proposed to benefit, a description of the water supplies proposed for mitigation together with any circumstances or limitations on their availability, and enough information for the Director to evaluate the factors below.

Notice and hearing. On receipt, the Director gives notice, holds a hearing as determined necessary, and considers the plan under the procedural provisions of Section 42-222, Idaho Code, in the same manner as an application to transfer a water right. That cross-reference is the practical one: it means protest, hearing, and a final order that can be taken up on reconsideration and then to district court.

The factors. Rule 43.03 lists fifteen factors the Director may consider in deciding whether a plan will prevent injury to senior rights, and says the list is not exhaustive. The ones that decide most plans are these:

• Whether the plan provides replacement water at the time and place required by the senior right, sufficient to offset the depletive effect of the ground water withdrawal. The rule directs that consideration be given to the history and seasonal availability of water, so that replacement is not required at times when the senior historically has not received a full supply.
• Whether compensation is provided during a shortage even though the effect of pumping is spread over many years and continues after pumping stops. Plans may use multi-season accounting, and must include contingency provisions if the mitigation source becomes unavailable.
• The reliability of the replacement supply over the term proposed.
• Whether the plan relies on artificial recharge of the aquifer, and if it uses computer simulation, whether the formulae and the aquifer values are generally accepted.
• Whether the plan calculates the consumptive use component of the ground water diversion reasonably.
• Whether it provides for monitoring and adjustment as necessary to protect the senior.
• Whether it allows later participation on an equitable basis by junior pumpers who do not join at the outset.

The last factor in the list is that the Director may consider whether the parties have reached agreement on a plan even if that plan does not otherwise fully comply with the rule.

Who mitigates in Idaho, and under which delivery call

Every Idaho mitigation plan hangs off a delivery call, with a handful of exceptions. IDWR's mitigation plan dockets, grouped by the call they answer:

The parties are ground water districts (Bingham, Bonneville-Jefferson, North Snake, Magic Valley, Madison, Jefferson-Clark, Big Lost River), irrigation districts (A&B, Falls, Southwest), cities (Pocatello, Idaho Falls, and the Coalition of Cities), food and water companies (J.R. Simplot, McCain Foods, Falls Water, Seapac), and individual operations. When an association files, it is usually mitigating for its whole membership at once.

The Idaho mitigation plan approval record

Of the 48 matters, 29 carry an order approving the plan somewhere in the filing trail and six carry an order dismissing one. The rest are pending, withdrawn, or resolved inside a broader settlement rather than by an approval order of their own.

These are the fifteen Idaho mitigation plan dockets still on IDWR's active list, with the date of the most recent order approving a plan on that docket.

Twelve of the 48 dockets have received a filing since August 2024, nine of them on the active list.

What an Idaho mitigation plan means for an operation

If you pump ground water on the Eastern Snake Plain, two questions decide your season: which plan covers you, and whether it is still in force. Where an irrigator is covered through a ground water district that filed on behalf of its members, that document sits on a docket the irrigator's own name does not appear on.

Three things follow from the rule itself. Replacement water has to arrive when and where the senior needs it, so timing counts alongside volume. Contingency provisions are mandatory if the mitigation source can become unavailable. And a plan may allow later participation on an equitable basis, so a junior who did not join at the outset can have a route in, on terms the existing participants negotiated.

New dockets keep opening for individual operations. Five of the fifteen active plans were filed in 2025 or 2026, and all but one of those five was filed by a company or a family rather than by a district.

What to watch in Idaho mitigation plans

Dockets numbered CM-MP-2026 are the current year's activity. Three have opened so far this year, two of them still active, and one already carries an approval order.

The 2026 Legislature wrote consumptive use limits for large industrial water users into statute for the first time, covered in the 2026 session summary. A statutory cap and a Rule 43 mitigation obligation are different instruments pointed at the same aquifer, and how they interact has not been tested.

Rule 43.03 lists managed aquifer recharge as a means of protecting pumping levels and compensating seniors, and the Idaho Water Resource Board runs the recharge program that most of that water moves through.